The president of the San Francisco chapter of the Hells Angels Motorcycle Club was shot and killed Tuesday night on a Mission District street, police said Wednesday.

Mark "Papa" Guardado, 45, was shot at 10:30 p.m. Tuesday near 24th Street and Treat Avenue, about a mile from the group's clubhouse where he lived. He died at San Francisco General Hospital.

Witnesses told investigators that Guardado and the gunman struggled before the shooting.

"They had a wrestling match first," said Lt. Mike Stasko of the San Francisco police homicide detail. Then "the guy shot him, and he got on his motorcycle and left."

Police have made no arrests, but said one avenue they are exploring was that Guardado was fighting with a rival in another motorcycle group. "We're looking at all the options," Stasko said.

An attorney who was defending Guardado in a battery case in Sonoma County said that he was "absolutely devastated" by the killing and that "Mark was a wonderful human being."

"His friends loved him," said the attorney, Patrick Ciocca. "He really was an all-around good guy. There are hundreds, if not thousands, of people who are going to miss him dearly."

Members of the Hells Angels at the group's clubhouse on Tennessee Street in the Dogpatch neighborhood of San Francisco declined to talk about the killing.

At the street corner where Guardado was shot, across from a bar and a nail salon, there was a makeshift memorial where someone had written in large, black letters, "RIP Papa Frisco."

Nearby, others wrote "never forget" and "we will always love you." Five burned-out candles lay nearby.

Ciocca was unable to say how long Guardado had headed the local chapter. But he stressed that the Hells Angels had been unfairly harassed over the years by authorities who have raided the clubhouse in search of evidence that the group is a criminal enterprise.

"It's outlandish," Ciocca said.

The group's San Francisco chapter - or "Frisco," as its members call it - is the second-oldest Hells Angels club in the country, after Fontana in San Bernardino County. In 2004, it celebrated its 50th anniversary with a party that attracted about a thousand bikers from around the world.

The Hells Angels have long feuded with another motorcycle group, the Mongols. In 2002, a brawl between dozens of members of the two groups in a Laughlin, Nev., casino resulted in the deaths of three bikers and 13 injuries.

Sonoma County beating

Guardado had an assault conviction in Massachusetts and served prison time there in the 1990s, but had no significant criminal record in California. When he died, however, he was facing charges in Sonoma County stemming from a beating outside a bar in Petaluma earlier this year.

Police said the incident happened Feb. 10 at McNear's Saloon & Dining House. Guardado bumped a bar patron, who was not a member of a motorcycle gang. The patron fled the bar, authorities said.

Once outside, the victim was surrounded, beaten and kicked by several other alleged members of the Hells Angels, prosecutors said.

Guardado started the attack for no reason, said Sgt. Jim Stephenson of the Petaluma police street crimes unit.

"We can't determine any motive - it was just what they do," Stephenson said. "It's just intimidation."

Guardado was charged with battery in furtherance of a street gang. Jonathan Nelson, 31, vice president of the Sonoma County chapter of the Hells Angels, was charged with felony battery in the incident.

S.F. clubhouse raid

In July, federal and local authorities raided the Hells Angels' clubhouse in San Francisco, and Guardado was arrested on suspicion of possessing illegal mushrooms.

Ciocca said authorities had been looking for evidence to support the premise that the Hells Angels was a criminal organization. They seized documents and some posters, but nothing that backed their suspicions, he said.

"They found nothing, at all, to further the idea that they were a criminal street gang," Ciocca said. "They were turning it into the crime of the century - it's ridiculous."

Attorneys for Guardado and Nelson had filed a joint motion in the Sonoma County case in which they asserted that the Hells Angels organization was not a street gang. They were challenging a court ruling that barred the defendants from wearing Hells Angels attire to court hearings.

A judge ultimately barred the defendants and onlookers from wearing any Hells Angels jackets or clothing in court, but did not rule on the issue of whether the organization constituted a street gang.

'Extremely dangerous'

Guardado "was an extremely dangerous gang member," said Victoria Shanahan, the Sonoma County prosecutor in the Petaluma case. "I find it interesting the fact that they were arguing they are not gang members, but this appears to be a gang-motivated killing."

Ciocca said that his client had a "warm heart and an outgoing personality" and that he last spoke to him two weeks before his death.

"We are disappointed that he will not have a chance to clear his name," he said.