On the night of February 16, 1970, Brian McDonnell was sorting through bulletins on the Teletype machine at Park Police Station in the Upper Haight neighborhood of San Francisco. The respected 44-year-old sergeant was checking results from the recent union elections, in which he was running for station representative. Steady winter rain fell outside. At 10:45 p.m., a bomb planted on the ledge outside a nearby window went off.

McDonnell took the brunt of the blast to his body and face. The bomb was packed with inch-long industrial fence staples, which severed his jugular vein and lodged in his brain. He would die two days later without ever regaining consciousness.

Investigators would later surmise that the explosion had been intended to coincide with the 11 p.m. turn of the watch, when roughly two dozen officers would be coming on or going off duty. As it was, many were still changing in the second-floor locker room. Rushing downstairs, they found Officer Frank Rath, who had been in the business office with McDonnell, stumbling dazedly around the room with his gun drawn. Blood and staples covered the floor.

"I was a Vietnam veteran. I'd been in a war," recalls retired police sergeant James Pera, then a 24-year-old patrol officer, who was one of the first on the scene in the minutes after the bombing. "But I never expected this to happen in my hometown, in a police station. It was something we never expected to see in our own country."

Awash in revolutionary and antiwar fervor, the Vietnam era was a dangerous time for cops. McDonnell was not American law enforcement's first casualty, and he would not be its last. Police continue to investigate his murder, which remains unsolved.

Information in the long-running investigation into the Park Station bombing has been closely held by law-enforcement officials, who still cling to hopes of bringing charges in the nearly 40-year-old case. Yet rumors have circulated for decades that the Weather Underground, a militant leftist group, was involved in the attack.

National interest in the Weather Underground was revived last year during the presidential campaign, when Republicans and conservative bloggers tried to smear Barack Obama for his ties to the group's former leaders, Bill Ayers and Bernardine Dohrn. A married couple now comfortably ensconced in the ranks of Chicago's liberal intelligentsia, Ayers and Dohrn were early political patrons of Obama's, hosting a campaign event for the future president in 1995 when he ran for the state Senate in Illinois.

Ayers and Dohrn assert today that the group deliberately avoided killing people in a campaign of "symbolic" bombings of empty government buildings. They and other former Weathermen have dismissed as a right-wing conspiracy theory any suggestions that their organization was responsible for the Park Station bombing.

Now, speaking publicly for the first time about the investigation, former FBI agents have told Village Voice Media the basis for their belief that the Weather Underground was behind McDonnell's murder. The agents have revealed that two credible eyewitnesses — both former left-wing radicals tied to the Weathermen — gave detailed statements to investigators in the 1970s alleging that Dohrn and Howard Machtinger, another member of the group, were personally involved in organizing the deadly attack. Both witnesses claimed to have participated in meetings where the bombing was planned, and one confessed to having cased the police station for the Weathermen prior to the explosion.

Working from these statements, authorities have quietly devoted far more attention to the Weather Underground in recent years than was previously known. Dohrn, Machtinger and Ayers were all targets of a secret federal grand jury investigation in 2003 into McDonnell's killing, according to San Francisco criminal-defense lawyer Stuart Hanlon, who has become familiar with the Park Station case while defending a client charged in another 1970s police murder. While indictments against the three were never issued, Hanlon says, "it was clear they were the targets. They weren't called — other people were called about them. The Weather Underground was the target of Park Station [investigators]."

The case against the Weathermen is far from complete. Still, given the multiple witnesses tying the group's former members to the killing of a police officer, some investigators say they are troubled by the impunity with which Ayers and Dohrn have peddled a version of the past wiped clean of bloodshed.

"I don't think they should be besmirched. I just think the truth should come out," says retired FBI Special Agent Willie Reagan, who investigated the Weathermen in the 1970s and served on a task force that reopened the investigation into McDonnell's murder in 1999. "There's so much there. If you've ever been in a courtroom, you know defense attorneys can create doubt about anything. But common sense tells you something. Who else could it be?"

Reagan, 68, has little in common with the partisan hacks who tried to make hay from Ayers' militant past during the 2008 election season. A gruff career undercover investigator who now lives in retirement north of San Francisco, he has deployed his talents for disguise and detection to help bring down extremist groups of all political stripes.

In the 1970s, Reagan grew out his hair and mastered the counterculture shibboleths of the New Left. His work as an undercover agent, or "beard," as they were known at the FBI, helped disrupt a 1977 plot by the Weathermen to bomb the office of John V. Briggs, a conservative California state senator. Years later, Reagan grew a beard again — this time for a stint undercover with the Freemen, a group of armed right-wing radicals who sequestered themselves on a Montana compound at the height of the militia movement in the 1990s. In between, he infiltrated drug organizations and the Mob.

"I worked the right wing as hard as I worked these nuts," he says of the Weathermen. "But the press kisses their asses, and a lot of the information isn't out there."

In 2000, Reagan was recruited out of retirement to join the Phoenix Task Force, a team of local and federal law-enforcement officials investigating unsolved cop killings from the 1970s, including the long-dormant Park Station case. Among his duties was sifting through the FBI's voluminous paperwork on the Weather Underground.

He soon came across a set of decades-old documents that astonished him. In the bulging case file on the Weathermen was a sheaf of FD-302 forms, used by bureau agents then, as now, to summarize interviews performed in the course of investigations.

The FBI's first recorded statements on the Park Station bombing plot came from interviews over two days in June 1972 with a man who once had been a writer for the Berkeley Tribe, an underground newspaper. While Reagan would not disclose the man's name, law enforcement sources with knowledge of the investigation said he is Matthew Landy Steen, who has used the alias William Hellis Coquillette.

Steen told agents he had attended a Bay Area meeting in January 1970 at which half a dozen Weather Underground activists discussed their plans to plant a bomb at Park Police Station. Among those Steen placed at the meeting were Dohrn, the Weather Underground's charismatic leader; and Machtinger, who investigators believed to be one of the group's principal bomb technicians.

Also in the case file were multiple forms from interviews with a former Weather Underground member named Karen Latimer. In the mid-1970s, years after Steen spoke to the FBI, Latimer came forward to say that she had attended a separate planning session for the Park Station attack with Dohrn and Machtinger in the winter of 1970. (In the months leading up to the bombing, Dohrn was living on a houseboat in Sausalito, just over the Golden Gate Bridge from San Francisco, according to an account in A Radical Line, the family memoir of Thai Jones, son of former Weatherman Jeff Jones.)

At these meetings, Reagan says, Dohrn "seemed to be more or less the ringleader," while "Machtinger gave instructions on how to build the bomb, and they discussed the placing of the bomb at Park Station."

Reagan says the witnesses' descriptions of the meetings were consistent with each other and strikingly similar to other Weather Underground planning sessions he had personally attended while an undercover agent. The idea, he says, was to implicate all members in a criminal conspiracy, reducing the chance that anyone would turn to the police.

"To them, building a bomb is an act of cohesion," Reagan says. "It's almost like the Mob when they ask someone to kill somebody or hack a guy's arm off. They trust you more when they're dirty with you."

Reagan's account was confirmed by Max Noel, another retired FBI agent who investigated the Weathermen in the 1970s while based at the bureau's San Francisco field office. "They did exist, and they were credible," Noel said of the statements.

San Francisco Police Inspector Joe Engler, the lead detective on the Phoenix Task Force, declined to comment on evidence or potential witnesses in the Park Station case, citing the ongoing investigation into the bombing. He referred a request for the forms on Latimer and Steen to federal authorities. At press time, the United States Attorney's Office for the Northern District of California said a Freedom of Information Act request from Village Voice Media for the documents was being reviewed by the U.S. Department of Justice in Washington D.C.

For decades, the only known indications of the Weather Underground's involvement in the bombing of Park Station had been tenuous hearsay from Larry Grathwohl, a U.S. Army veteran who was hired by the FBI to infiltrate the Weathermen in 1969. In sworn testimony before the U.S. Senate Judiciary Committee in 1974 and in a 1976 memoir, Bringing Down America: An FBI Informer with the Weathermen, Grathwohl asserted that he had heard from Ayers during a meeting of a Weather Underground cell in Buffalo, New York, that Dohrn "had to plan, develop and carry out the bombing of the police station in San Francisco." But former Weathermen have long dismissed his story as a fabrication. During a book tour of the Bay Area in January, Ayers told the San Francisco Chronicle that Grathwohl was "a paid dishonest person."

Reviewing the bureau's files in 2000, however, it was plain to Reagan that the case against the Weathermen went well beyond a solitary piece of after-the-fact hearsay relayed by an FBI mole. When he read the statements from the other two informants, who had independently supplied similar details about Weather Underground members conspiring to bomb Park Station, he had one thought: Why didn't they prosecute?

It turns out that law-enforcement officials had come much closer to pouncing on the Weather Underground than Reagan realized. In fact, according to another investigator familiar with the case, prosecutors came within a hair's breadth of filing charges against the group in the 1970s based on Latimer's testimony alone.

An articulate young woman with short dark hair who had joined the Weathermen after getting involved with the antiwar movement at Michigan State University, Latimer wore a tan pantsuit on the day she met with San Francisco detectives in a Financial District hotel room. According to the investigator with knowledge of the case, she had come forward to betray her former comrades in the revolution in order to have a federal hold on her passport lifted so she could travel abroad and was delivered to the SFPD by FBI agents. She was willing to testify in court if granted personal immunity from prosecution.

Listening to Latimer calmly narrate the planning of the Park Station attack, step by step, the local detectives knew they finally had a break. In fact, they believed she could make their whole case. Latimer claimed to have personally cased the station and could describe the package that had held the explosive device before it had gone off. "It was just too detailed," the investigator familiar with the case recalls. "It was A to Z without leaving out L and M. I was convinced."

The day after interviewing Latimer, the investigator says, the detectives hastily convened a conference with San Francisco District Attorney John Jay Ferdon and a federal prosecutor. At that meeting, the police officers and federal prosecutor argued for granting Latimer immunity and proceeding to file charges. (It is unclear which Weather Underground members would have been named as defendants or whether the D.A. and U.S. attorney were aware of Steen's earlier statement to police.)

Ferdon opposed this plan, arguing that Latimer's sudden appearance could be a ploy. Once she was granted immunity, he feared she would simply change her story and confess to planning and executing the bombing alone, clearing herself and her former comrades of criminal liability. He won the argument, and local detectives renewed their efforts to find more evidence or informants to support a prosecution.

Caution in filing charges based solely on Latimer's statements may have been warranted for other reasons. Testimony from criminally implicated informants is notoriously problematic for prosecutors, who must explain to a jury why their witnesses aren't merely lying to avoid more severe punishment. Hence the need, in an ideal world, for more extensive corroboration of what happened the night of the bombing or physical evidence — in the form of fingerprints or ballistics — to back up Steen's and Latimer's stories.

Such evidence has never been uncovered in the McDonnell murder case. After the launch of the Phoenix Task Force, a forensics expert at the California Department of Justice was able to develop a latent fingerprint on a fragment of the Park Station bomb using new scientific techniques, according to an affidavit filed by Engler in another of the task force's cold cases. But the print was still too undefined to be used for identification.

The FBI's witness statements are also less comprehensive than investigators would like. For instance, neither Steen nor Latimer said they had been present for the construction of the bomb (though Reagan said at least one of them reported seeing bombmaking materials, such as detonator cord, at the planning session) and neither had seen who placed the device on the station's window ledge.

And then there is the most vexing obstacle to a successful prosecution of the Weathermen based on former collaborators' confessions — the inconvenient fact that an entirely different set of militant activists has also claimed credit for the bombing.

On August 28, 1971, Anthony Bottom and Albert Washington, cadres of the violent Black Panthers splinter group known as the Black Liberation Army (BLA), pulled up in a car alongside the patrol cruiser of San Francisco Police Sergeant George Kowalski at an intersection and leveled a submachine gun at him. The BLA was suspected or convicted of multiple attacks on police officers in the 1970s, including the 1971 shotgun killing of Sergeant John Young at San Francisco's Ingleside Police Station. On this occasion, however, they were unsuccessful. The gun, loaded with the wrong type of ammunition, jammed. Bottom and Washington were arrested and charged with attempted murder.

Over the next month, Bottom, while in police custody, made an extraordinary series of statements, according to investigators familiar with his case. He reportedly told SFPD homicide inspectors Frank McCoy and Eddy Erdelatz that he had personally planted the bomb that killed McDonnell at Park Station and said he had helped plan the Ingleside attack, which took place while he was in jail. He also claimed involvement in the bombing of St. Brendan's Church in San Francisco during a police funeral in October 1970 and in a plot to plant sticks of dynamite on the roof of a police station.

When he made his far-ranging confession, Bottom was already destined for prison. A revolver found with him at the time of his arrest had been traced to New York City police officer Waverly Jones, who was gunned down with his partner, Joseph Piagentini, by BLA members in a Manhattan housing project that May. Today, Bottom is serving a life sentence for his conviction in their murders at Auburn Correctional Facility in upstate New York.

A number of law-enforcement officials with knowledge of the Park Station case view a BLA link to the bombing with skepticism. Bottom, in particular, was famous among detectives of the era for his big mouth. "He was just a guy who liked to hear himself talk," one investigator says. "We could not corroborate independently what he told us about Park." Another former investigator connected to the case is more blunt: Bottom, he says, "would confess to the quake of '89."

Mark Goldrosen, a San Francisco attorney who represented Bottom when he was charged in 2007, with seven other defendants, for the 1971 attack on Ingleside Station, concurs with investigators' dismissive takes on his client's statements about the Park bombing. "If he had admitted it, and if it was considered credible, this would have been prosecuted a long time ago," he says.

Another former BLA member, Ruben Scott, also told police in the 1970s that the organization was involved in the Park Station killing, according to law-enforcement sources. Scott reportedly said that he was not personally present the night of the bombing.

The BLA connection to Park Station may be a red herring — or it could mean that McDonnell's murder was simply the result of two militant groups working in tandem. A prime tenet of the Weathermen's through-the-looking-glass revolutionary doctrine was that it was their duty to shed "white-skin privilege" and put themselves at the service of black radicals, and there are indications that the affinity between the BLA and Weathermen was particularly strong.

For example, the BLA collaborated with former Weather Underground members Kathy Boudin and David Gilbert in a 1981 armed robbery in Nanuet, New York, that ended with the deaths of two police officers and a Brink's armored truck guard. Ayers and Dohrn have also expressed their fondness for members of the BLA in surprisingly personal ways. Their son, Zayd Dohrn, is named after BLA member Zayd Shakur, who died in a shootout with New Jersey state troopers in 1973.

From today's vantage point, the spectacle of so many revolutionary groups competing to blow up or shoot sworn peace officers might seem strange. But in the late 1960s and early 1970s, America's major cities were in something close to a guerrilla war. In 1972 alone, the FBI attributed 1,500 bombings within the United States to "civil unrest" from domestic radical groups. Noel, the retired San Francisco FBI agent, says police officers routinely searched their patrol cars for bombs before starting their engines.

In this environment, many law-enforcement officials resorted, with unfortunate results, to dubious practices of their own. The most notorious example of police overreach from the era was doubtless the FBI's COINTELPRO, an elaborate program of domestic espionage that targeted peaceful civil-rights groups alongside the Black Panthers and the Weathermen. Senate hearings on the program in the late 1970s concluded with a formal denunciation of such FBI tactics as wiretapping and illegal property searches.

The rise and fall of the Weather Underground is one of the more outlandish chapters in the phantasmagoria of Vietnam-era radicalism. Formed in 1969 as a militant faction of the mass antiwar movement Students for a Democratic Society (SDS), what was then commonly called the Weathermen — named after the Bob Dylan lyric, "You don't need a weatherman to know which way the wind blows" — proclaimed a desire to foment what they saw as an imminent, global communist revolution within the U.S. Their motto: "Bring the war home." (After the winter of 1970, "Weathermen" became the Weather Underground, a nod to the group's fugitive status and disdain for sexist pronouns.)

In December 1969, the group convened a "war council" in Flint, Michigan, announcing its plans to attack institutions of the United States government and oppose "everything that's good and decent in honky America," according to an account of the meeting by former Weatherman Mark Rudd in his memoir, Underground. Rudd goes on to recount his own contribution to the proceedings: "It's a wonderful feeling to hit a pig," he told the group, using the '60s slang term for a police officer. "It must be a really wonderful feeling to kill a pig or blow up a building." Presiding over the meeting was Dohrn, the mercurial beauty FBI Director J. Edgar Hoover once called "the most dangerous woman in America."

The University of Chicago-educated Dohrn was a diva of the radical left, known for her shrill revolutionary creed. "We're about being crazy motherfuckers," she announced at the war council. Raising four fingers in what became known as the "fork salute," she praised the acolytes of cult leader Charles Manson for stabbing pregnant actress Sharon Tate in the stomach with a fork when they killed her in 1969.

This darker phase of the Weathermen lasted through March 6, 1970, when three members of the group were killed in an accidental explosion while building a bomb at a Greenwich Village townhouse. That bomb, members of the group would later reveal, was intended to cause a massacre at an Army dance in Fort Dix, New Jersey.

Following the townhouse explosion, the Weather leadership convened a summit at a beach house on Northern California's fog-hung Mendocino coast. At that conference, they decided to alter their bombing campaign, targeting only empty government facilities, according to Rudd's memoir. Now in hiding or "underground" because of riot and conspiracy charges, the Weathermen went on to claim responsibility for setting small bombs at the Pentagon, the U.S. Capitol and the State Department, none of which resulted in loss of human life.

Significantly, the attack on Park Station falls within the narrow period between December 1969 and March 1970 when the Weather Underground was still loudly devoted to killing people.

"During that ten weeks, they were intending, by their own statements — many statements — to commit acts of violence against persons," says Todd Gitlin, a Columbia University journalism professor and former SDS president who has written extensively on the history of the 1960s. Gitlin admits that he had no direct knowledge of the Weathermen's actions during the time in question, but says the bombing would have fit their M.O.: "It would have been consistent with their pronounced strategy during February 1970 if they had been involved in Park Station."

Resurfacing at the end of the decade, many of the Weathermen saw charges against them dropped or resolved with meager penalties because of the questionable FBI tactics used against them. Some went on to rehabilitate themselves through careers in academia. Dohrn is now a professor at Northwestern School of Law, and Ayers is an education professor at the University of Illinois at Chicago. Machtinger became a teacher in North Carolina. No former member or associate of the Weather Underground has ever publicly acknowledged a role in the Park Station bombing.

Dohrn, Machtinger and Ayers did not respond to repeated requests for comment for this story. Brian Flanagan, a New York City resident and former Weather Underground member who has condemned the group's tactics as misguided, denied that any Weathermen had carried out the bombing. "There's nothing that I have for you on Park Station, except that it was not the Weather," he says. "I'm absolutely positive." He declined to say whether he was in San Francisco when the attack took place: "That's as far as I'm going to go."

Rudd, who once held a leadership position in the group, says he didn't think the Weathermen had a hand in the murder of McDonnell, but acknowledges that he could not be sure, since he was not based in California at the time of the bombing.

"It's my impression that Weather Underground was not involved in that at all," he says in a telephone interview from New Mexico, where he now lives. "I was on the East Coast at the time, but I was still high enough in the organization. I never heard anything about it. Not only that, I was in a position to know." He adds, "Of course, that's not any kind of exculpatory evidence."

If the Weather Underground was involved in the attack on Park Station, the group's denials or silence on events during the winter of 1970 would make sense, at least from a legal perspective. Unlike the bloodless bombings the Weathermen carried out in the mid-1970s, murder and related conspiracy charges carry no statute of limitations. In other words, if prosecutors opted to file charges in the Park Station bombing, Dohrn, Machtinger and any others implicated in the attack could be hauled into court.

Meanwhile, veteran investigators still fume over the ease with which Ayers and Dohrn have assumed the mantle of middle-class respectability. When people talk to Noel about the Weather Underground's avowed intent not to harm people, he likes to tell the story of a 1971 search of one of the group's principal "safe houses," an apartment in San Francisco's Nob Hill neighborhood. Inside, FBI agents and SFPD inspectors discovered C-4 explosives, voice-activated bomb switches and concealable shivs made from sharpened knitting needles epoxied into the caps of ballpoint pens.

"'Voice-activated switch' means the bomb goes off when a person comes in and talks," Noel says. "This whole image that these were nice-type people is what makes me upset. It's bullshit. That's not what they were. They were thugs, and they were criminals trying to overthrow the U.S. government." During the 2008 election season, Noel even made a brief televised appearance with Greta Van Susteren on FOX News to counter the arguments of Weather Underground apologists who were saying the group had been essentially nonviolent.

Noel, Reagan and other law-enforcement officials interviewed for this story still hold out hope that the Park Station case will one day bring a reckoning for the Weathermen. But the specter of the Vietnam era's radical legacy should be summoned with care, as another prominent cold case from the same period illustrates.

In 2007, the California Attorney General's Office filed charges against eight alleged former Black Liberation Army radicals — Bottom among them — for the attack on Ingleside Police Station and the murder of San Francisco Police Sergeant John Young in 1971. The same Phoenix Task Force that reopened the Park Station investigation was responsible for building the case on the Ingleside attack.

After lengthy litigation and an outcry from liberal activists over the belated prosecution, charges against five of the defendants were dropped. An additional two, including Bottom, pleaded guilty to lesser charges and received probation — hardly a meaningful punishment for someone serving a life sentence. Charges against the eighth and last defendant have yet to be resolved, but by most accounts, the case has been a huge disappointment for cold-case investigators and a humiliation for the state attorney general's office.

According to San Francisco defense attorney Hanlon, who represented one of the Ingleside defendants, the documentation he's seen on Park Station doesn't bode for better results. "I've looked at probably 90 percent of the evidence," he says, explaining that much of it was available to Ingleside defense attorneys because of the BLA's possible connection to the bombing. "They have no case, and that's why they have no prosecution. They have enough snitches. They just don't have any evidence."

Investigators privately acknowledge that, as time passes, a conviction seems more improbable. Steen, one of the two former radicals who described the Weather Underground's alleged planning of the Park Station bombing to the FBI, apparently became a homeless drifter. It is unclear whether he would still be a competent witness. A 2002 SFPD bulletin seeking him as a witness in a criminal conspiracy investigation states that he was "transient," last encountered by police during a 2000 arrest for squatting in Golden Gate Park. Steen could not be reached by Village Voice Media for comment.

Latimer, who would likely have been a star witness for the prosecution, died several years ago, according to Reagan. During his brief return to the Park Station case in 2000, Reagan says, he re-established contact with Latimer, whom he had known during his years as an undercover agent in the 1970s. Speaking to her again after the intervening decades, he found her deeply frustrated that her decision to cooperate with law enforcement so many years ago had been of little consequence.

"She was looking for a form of justice, and she was totally disappointed that there wasn't enough to prosecute," he says. "To her, it was a reality. She was there, and she heard them talking about doing this."

But the Weathermen, fugitives for the better part of a decade, haven't lost their knack for evading the scrutiny of the law. At a preliminary hearing earlier this year in the failed Ingleside murder case, Dohrn, in a gesture of solidarity among aging radicals, traveled to San Francisco from Chicago to stand with the defendants' supporters in the courtroom. Engler, head of the Phoenix Task Force, was also present. He recognized and approached her, according to law-enforcement sources who described the scene.

Engler introduced himself to Dohrn as a San Francisco homicide detective and said he would like to speak with her after the hearing. She greeted him politely, but was noncommittal, and left without giving him a chance to interview her when the courtroom session ended. It had been 39 years since Park Station was bombed. Police were still looking for a break. And once again, Bernardine Dohrn had disappeared.

Peter Jamison is a staff writer at SF Weekly,

RFT's sister paper in San Francisco.

Send feedback to letters@riverfronttimes.com