Dr. Rahmatollah Sedigh Sarvestani is dying. The Iranian sociologist, recently retired from a long teaching career at the University of Tehran, suffers from prostate cancer and a pelvic tumor. With his kidneys failing after chemotherapy, doctors in Tehran have stopped treating him.

His last hope is to come to the U.S., where his wife and children are, and where doctors say he could receive potentially life-saving treatment.

But the U.S. won't let him in. And they won't say why.

In March, Sarvestani's visa request was denied. The consulate cited a clause in the Immigration and Nationality Act: Activity "relating to espionage or sabotage." No further information is provided.

"We were absolutely shocked," said his daughter Sahra. "My father is a sociologist. He has cancer."

Sarvestani, who is 64, has recently been confined to a wheelchair and weakened by severe anemia. Sahra says she can barely hear him on the phone: "I would assume he would need to talk and move to spy on the U.S."

The family has made a last-ditch effort to bring him here on humanitarian parole — a short-term, discretionary travel permit for extraordinary circumstances. The family has collected dozens of letters of support from academic colleagues and family members in the U.S., as well as one from his daughter Soureh's congressman, André Carson, D-Ind.

The U.S. could have incriminating information on Sarvestani. But without knowing the details, the family doesn't know how to respond to them.

Instead, they are left to speculate. Sarvestani studied at University of Akron, in Ohio in the 1970s. Two of his daughters were born in the U.S. Like many Iranian students at the time, he supported the overthrow of the Shah and the Iranian Revolution. He belonged to a student group that organized protests in support of Ayatollah Ruhollah Khomeini.

But traveling to the U.S. hadn't been a problem before — Sarvestani spent a sabbatical year in California in 1994. And more recently, Sarvestani has been an open critic of the Iranian government.

"I can't believe they are dismissing his application over something that happened three or four decades ago," said his son, Hadi, who works at a law firm in Indiana. "It's at the point where he's so ill it takes multiple people to care for him, multiple people to get him out of bed. It's baffling." (ProPublica was not able to speak directly with Sarvestani. We reviewed supporting documents and interviewed former colleagues, students and others.)

In denying a visa, the State Department is required only to cite the relevant provision of the law, not provide evidence or rationale. That is the case for all denials, not just those related to national security.

There is also almost no way to appeal a visa decision. A precedent known as the doctrine of consular non-reviewability holds that they can rarely be challenged in court.

Spokesmen for the State Department and the U.S. Citizenship and Immigration Services told ProPublica they could not comment on individual cases.

Sarvestani was known for his work on poverty, drug addiction, and urban spaces. His students recall him as religious and politically moderate. His ties to officialdom, according to his family, are limited to work for the Iranian Olympic Committee, and acquaintances among the upper echelons of academia in Iran, such as Mohammed Javad Zarif, a former colleague at the University of Tehran and previously Iran's envoy to the U.N.

His son Hadi said that if his father felt a sense of duty, "it was to the academic world in Iran, to the doctoral students he was close to, and to his position of academic leadership."

According to Sarvestani's wife, Mahboobeh Ayatollahzadeh, Islamic student groups regularly criticized him as pro-Western. In 1985, a hardline Islamic student group campaigned against Sarvestani's appointment as dean of social sciences at his university. The group circulated pamphlets tying him to the U.S. and mentioning his family, who are Baha'i, a persecuted religious minority in Iran. He was forced to step down, eventually returning as a regular faculty member. (Ayatollahzadeh is a school psychologist in Indianapolis, but is currently in Tehran, caring for her husband.)

Sarvestani began keeping a blog in August 2008, where he wrote academic and social commentary, including often barbed invectives directed at members of the Iranian government.

Reza Akbari, who chronicled the Iranian blogosphere on the website InsideIran, characterized Sarvestani's stance as liberal for Iran.

"He could express critical views of the government because of his academic credentials, because he was very well respected," said Dr. Zohreh Bayatrizi, a former student who is now an assistant professor of sociology at the University of Alberta.

"During the election it got so dangerous. I would call him, crying, and say please don't post anything about this on the blog," recalled Sarvestani's daughter Sahra.

The government shut down the blog in July 2009, shortly after Mahmoud Ahmadinejad won re-election. (The disputed vote sparked widespread protests from the reformist opposition, which came to be known as the Green movement. Bayatrizi remembered Sarvestani coming to class with a green armband.)

Last year, Sarvestani was pressured into retiring early from the university. After 2009, said Abbas Milani, director of Iranian Studies at Stanford University, the government "went methodically through and purged members of the Green movement." Iran has also made a concerted effort to rid the educational system of Western influences.

Sarvestani has also experienced personal tragedy. In 2006, his mother was found murdered in her home. No investigation was conducted, but the family believes it was because she led Baha'i prayer meetings.

His family has not yet told Sarvestani that the U.S. denied his visa because of "espionage."

He is "weak and highly vulnerable, both physically and emotionally," his daughter Soureh wrote in a letter submitted with his parole application.

After the 9/11 attacks, the U.S. began to treat immigration and visas as a front line in counterterrorism. Iranians, whose country has long been designated a state sponsor of terrorism, have faced particular scrutiny.

Trita Parsi, founder and president of the National Iranian American Council, said that his organization frequently receives complaints from Iranians perplexed by visa denials. "You've already got Iranian passport. That's a red flag," Parsi said. "Then you have something in the past, and that's another red flag. Too many red-flags and that's it."

Last year, the State Department denied 268 visas under the espionage clause, more than double the number from five years ago. In 2001, there were just 19 such denials. The State Department doesn't provide denial statistics by nationality. But earlier this year, Bloomberg reported at least six Iranian engineering students denied visas under the espionage clause.

If a consular officer has concerns about an application, the officer requests input from intelligence agencies. Consulates now request these reviews with increasing frequency, according to Edward Alden, a senior fellow at the Council on Foreign Relations. Before 9/11, he says, there were a few thousand a year. In the financial year 2011, there were 366,000, according to figures provided to Congress by the State Department this March.

The review, which must be repeated each time a visa is sought, also often causes delays in visa decisions.

Sarvestani has waited nearly nine years. He first applied for permanent residence through his daughter Soureh, a U.S. citizen, in 2003. In 2009, finally, the application was approved — a good sign, the family thought. But after an interview with a State Department official in Turkey, and more waiting, the denial arrived this March.

Sarvestani's lawyer, Denyse Sabagh, has represented several other clients whose visas were denied under other national security grounds, such as material support for terrorism. In most cases, she said, it was near-impossible to figure out what the exact issue could be, let alone challenge it.

This spring, Sarvestani's family filed Freedom of Information Act requests to try to determine the block on his record. In September, the FBI wrote to say it had more than 2,000 pages of potentially responsive documents. They haven't been released yet, but there is evidence that the agency has long investigated the student group that Sarvestani belonged to in the U.S.

Sarvestani arrived in the U.S. in 1977, a tumultuous period in U.S.-Iranian relations. The shah — who had come to power in a U.S.-backed coup — faced mounting protests. He fled the country in January 1979, and by the end of that year Iran was an Islamic republic under Khomeini.

During these years, Sarvestani belonged to the Muslim Students Association Persian Speaking Group (MSA-PSG), comprised mostly of Iranian Shiite Muslims in the U.S. (and sometimes known as Anjoman Islami, the Farsi phrase for an Islamic student group). According to Sarvestani's family, he went to demonstrations, ran a call-in news hotline, distributed Iranian media to the diaspora, and organized sales of religious books. He also acted as a liaison between bickering factions of Iranian students, traveling frequently to other centers of Iranian life to mediate confrontations.

In August 1980, as the hostage crisis at the U.S. Embassy in Tehran stretched on, Sarvestani joined about 50 members of MSA-PSG staging a hunger strike in front of the White House. They were protesting alleged mistreatment of pro-Khomeini demonstrators arrested in D.C. in late July.

Federal investigators told reporters at the time that the demonstrations were funded by Iran, which MSA-PSG denied.

Hamid Algar, a professor at University of California, Berkeley, who has written on Iranian Islamic groups, says that MSA-PSG did not have formal ties to the government, but was "thoroughly in support of the revolution."

According to the family, most of Sarvestani's colleagues in MSA-PSG returned to Iran, and Sarvestani had only periodic contact with the U.S. group once he left. The Sarvestani children all went to Catholic school in the U.S., where Sarvestani's wife had the children attend Mass daily, though the school did not require it. (She has long worked on interfaith educational initiatives.)

Today, MSA-PSG continues to hold a yearly conference. A photo of Iran's Supreme Leader Ali Khameini adorns one corner of its website, an Iranian flag the other. The most recent public statement from a government official on the group is Senate testimony by then-FBI Director Louis Freeh in 1999. He described it as "comprised almost exclusively of fanatical, anti-American Iranian Shiite Muslims," which "the Iranian government relies heavily upon...for low-level intelligence and technical expertise." In 2004, the New York Times profiled an Iranian-American couple that was fired from government jobs after failing a security check, apparently because they had attended MSA-PSG conferences in the late 90s. Beyond Freeh's statement, there is no public evidence linking MSA-PSG to criminal activity.

When Sarvestani returned to school in Akron after the White House demonstration, his department chair told him the FBI had questioned them about his activities. Sarvestani assured his boss he had done nothing illegal.

Shortly before Sarvestani returned to Iran in 1984, according to his family, he was also approached by U.S. government officials who said they had observed his work as a student organizer and would like for him to stay in the U.S. Sarvestani skipped a follow-up meeting at the Chapel Hill Mall, in Akron, and returned to Iran as planned. Soon after, Sarvestani's in-laws received an envelope from the U.S. addressed to Sarvestani. Inside was a greeting card with the printed line, "hope we get together real soon." Beneath it, written in block letters: "AT CHAPEL HILL MALL." Sarvestani still has the card.

None of this seemed to matter in 1994. That year, Sarvestani returned to the U.S. for a yearlong sabbatical in California, during which he translated a book on coaching strategies into Farsi. (Gary Walton, the book's author, remembers him fondly. Sarvestani arranged for Walton to give a seminar to Iranian Olympic coaches in 1997, Walton says, but the State Department advised against it.)

Sarvestani's wife, Ayatollahzadeh, says that when processing their visas for the sabbatical, their consular office said that her husband was "on a list," but that he would approve their visa anyway. Sarvestani returned to Iran the following year, leaving behind Ayatollahzadeh, who was by that time pursuing her own PhD, and all of the children.

The plan was for Sarvestani to join them after a few more years. It has been 17.

Ayatollahzadeh and the children now take turns traveling to Iran to care for Sarvestani. They worry constantly about their safety or that one of them will be stranded in Iran with visa troubles of their own. They have nearly exhausted leaves from work, says Sarvestani's eldest daughter Sahra, who is a professor of electrical and computer engineering at the Missouri University of Science and Technology. (A permanent resident of the U.S., she has done work for the Department of Defense.)

After doctors in Iran found the pelvic tumor this summer and ceased treating either cancer, the family sought out second opinions in the U.S. Several oncologists reviewed his case and said Johns Hopkins in Baltimore could offer, as one doctor wrote, "novel treatments unavailable in Iran or neighboring countries." Postponing treatment "will significantly reduce this patient's chance of survival."

Humanitarian parole is a discretionary, temporary permit based on either extreme need or pressing public interest, to be turned to if no ordinary visa is available. It is not the same as asylum, or refugee status. There is no appeal, and no reason given for a decision. Roughly 25 percent of the humanitarian parole requests received each year are approved, according to a Citizenship and Immigration Services spokesman. Last year, there were 1,500 applications.

The family applied for parole right after his visa was denied, on the basis of financial and emotional hardship, but was denied. They applied again last month, citing urgent medical need.

For now, Sarvestani waits in Iran. His daughter Soureh, who recently returned from a visit, says he is receiving only minimal medical attention, as his doctors consider him "incurable." On top of the cancers, Sarvestani is an amputee and now suffers blood clotting. Obtaining prescriptions and medical equipment in Tehran can be a costly bureaucratic nightmare. Back in the U.S., Soureh, who is a computer specialist for Indianapolis Public Schools, says it fills her with guilt to "simply pull up to a CVS drive-thru window. Medical care in Iran and the U.S. is like night and day."

Soureh brought her two-year-old daughter Fatimah with her to Iran — Sarvestani's only grandchild. They spent long hours together in Tehran. Now, Internet bans have made video chats difficult, so Soureh lets Fatimah chatter on the phone with him.

"My father is a gentleman and a scholar," Soureh wrote in a letter alongside photos of Sarvestani and Fatimah. "This is a plea for human dignity."