BOSTON --Months before the 2013 terror attack on the Boston Marathon, accused bomber Tamerlan Tsarnaev posed in front of a black flag often associated with jihad with a fellow worshiper at a Boston-area mosque, according to an FBI report obtained by ABC News.
The FBI report, which did not include the photo, describes Tsarnaev and his friend Khairullozhon Matanov as "seated in front of a black flag with a sword and a shadada phrase," referring to the Muslim statement of faith, and adds that the photo was taken "at the mosque." Similar flags have become symbols of jihad, used by al Qaeda and al Qaeda-linked extremist groups.
The FBI had been warned by Russian intelligence in 2011 that Tsarnaev may have become radicalized, but the bureau dropped its inquiry months before the photo was taken because it said it "did not find any terrorism activity."
The black flag picture is part of the evidence prosecutors said Matanov deleted from his computer to obstruct the investigation into the bombings, which in turn led to the arrest of the Kyrgyzstani national last month on federal charges. He has pleaded not guilty and is currently being held without bail.
The FBI report says the alarming photograph was taken on Eid-Al-Adha, also known as the Festival of Sacrifice, the highest of Muslim holidays, but does not say exactly when. A source familiar with the investigation told ABC News it was taken during the August 2012 celebration. The FBI report does not identify the mosque where the photograph was taken.
Tsarnaev and Matanov prayed at a mosque in Cambridge, Mass., the FBI report says, but Yusufi Vali, the Executive Director of the Islamic Society of Boston that opened the mosque told ABC News there were no reports of the black flag of jihad being at the 2012 Eid holiday, or at any other time. Tsarnaev had been asked to leave the Cambridge mosque after he disrupted services later that same year.
"Without doubt there is no symbol of violence or terrorism at the [Cambridge] center," said Vali. "I can confidently say that we preach moderation in line with more American values."
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The Islamic Society of Boston opened its first mosque in 1994 on Prospect Street in Cambridge in a former Knights of Columbus building. A larger $15.6 million Roxbury mosque opened in 2009. Because of its size, high holidays, like Eid, are celebrated there, Vali said.
Before Tamerlan Tsarnaev began to pray at the Cambridge mosque, which he did more frequently than his younger brother and alleged Boston bombing co-conspirator Dzhokhar, the Islamic Society of Boston over the years had had a small number of run-ins with alleged would-be violent extremists.
The Islamic Society of Boston was founded by Abdulrahman Alamoudi, who pleaded guilty in 2004 to charges related to his "activities... with nations and organizations that have ties to terrorism" -- including a link to an assassination plot targeting Saudi Arabian Crown Prince Abdullah ibn Abdilaziz, according to the Department of Justice. He was sentenced to 23 years in prison. To this day the FBI lists Alamoudi's prosecution as a "Major Terrorism Case" on its website.
Tarek Mehanna, 31, was a pharmaceutical student at a Massachusetts college where his father worked as a professor, and lived with his parents in upscale Sudbury where his mother ran a state-licensed day care center out of her home. He was convicted in 2012 of supporting al Qaeda and conspiring to kill Americans. Before that, Mehanna had visited the Cambridge center for prayers and lectures, in addition to visiting mosques in other parts of the state, Vali said.
After the Boston bombing, investigators found a Tarek Mehanna prayer card tucked into a Russian dictionary in Tamerlan Tsarnaev's Cambridge apartment, according to court documents.
Mehanna's alleged accomplice, Ahmad Abousamra, also occasionally prayed at the Cambridge mosque. He had graduated from the prestigious Catholic high school Xavier with honors and his father, Dr. Abdul Abousamra, was a respected endocrinologist at Massachusetts General Hospital before moving to Detroit and was the President of The Islamic Center of New England, according to The Boston Globe.
After being interviewed by agents from the FBI's Joint Terrorism Task Force, Abousamra was able to slip out of the country in 2006, according to the bureau. He was indicted in 2009 and last December he was added to the FBI's Most Wanted Terrorists List with a $50,000 reward for information leading to his capture.
Perhaps most controversial of the group, Dr. Aafia Siddiqui also prayed at the Prospect Street mosque while she earned a scientific doctorate degree at MIT. She eventually moved overseas with her husband and two children. She was detained in 2008 after Afghan officials found her in possession of handwritten notes that referred to a "mass casualty attack" along with a specific list of targets like the Statue of Liberty and the Brooklyn Bridge.
As military intelligence officials and FBI agents questioned her at a police compound in Afghanistan, prosecutors said, she grabbed an assault rifle from a U.S. serviceman and opened fire on her interrogators while saying "Death to America," according to the reported testimony of witnesses. No one was killed in the sudden attack. Siddiqui was convicted in 2010 on federal terrorism charges and sentenced to 86 years in prison.
Director Vali insisted that all were "infrequent" worshippers at the Cambridge center, as were the Tsarnaev brothers, and they also worshipped at other mosques. Their affiliation with the Islamic Society of Boston should not cast aspersions on either the Cambridge center or the larger Roxbury mosque, where some 1,200 worship every week, Vali said.
"When the [Boston] bombings happened initially, like most Bostonians, we were all traumatized and scared. We were devastated that these people were part of city and part of our mosque," he said.
The mosque was also where Matanov met Ibragim Todashev, a suspect in a mysterious triple murder elsewhere in Massachusetts, the FBI report says.
On Sept. 11, 2011, the ten-year anniversary of the 9/11 terror attacks, the bodies of three young men were discovered with their throats slit and covered in marijuana in a home in Waltham, Mass.
Todashev, a suspect in the case, lived with Matanov at the time of the murders, according to FBI reports, and later moved to Florida.This May Todashev was killed in his Orlando home by an FBI agent after he allegedly attacked the officer. The FBI says Todashev was on the verge of signing a statement that implicated himself and Tamerlan Tsarnaev in the triple murder. The same month, ABC News reported investigators had developed "mounting evidence," bolstered by "forensic hits," that pointed to the possible involvement of the Tsarnaev brothers in the grisly unsolved murders.
Matanov's immigration attorney, Paul Glickman, said that his client was cooperative with the FBI during multiple interrogations over the past year and answered all of the bureau's questions about the night of the Waltham murders.
"Mr. Matanov was cooperative multiple times," Glickman told ABC News. "I have no idea why he has been arrested now."
Glickman refused to comment on the specifics of his client's interviews with the FBI, including at least one that took place at his Boston office, according to the reports.
Matanov and Todashev have not been implicated in the Boston bombing, but Matanov did have dinner with the Tsarnaev brothers the day of the Boston bombing and texted Tamerlan roughly 40 minutes after the deadly blasts, prosecutors said. He was also in touch with Todashev in Florida after the attack, the report states.
Edward Hayden, who represents Matanov on the current obstruction charges said his client is a hardworking immigrant with dreams of bringing his family to the United States, not a radical.
"Being friends with someone is not an indication of terrorist activities," he said. The FBI report obtained by ABC News notes that Matanov told investigators he consciously avoided discussing extremism with the Tsarnaevs.
The Islamic Society of Boston said too that terrorism is are not in line with the mosque's values. Vali pointed out that mosque leaders volunteered to try and negotiate with Dzhokhar Tsarnaev, the accused bomber who survived the police shootout that took his older brother's life and who was on the run for hours before being captured.
"Since the bombing what we are intentionally trying to do at that Cambridge center is to push the right vision of Islam, in a stronger way... contributing positively to our community,'' Vali said. "That's what we are about."
Michele McPhee is a freelance journalist and frequent ABC News contributor based in Boston.CLICK HERE to return to the ABC News Investigative Unit homepage.