FBI agents have begun questioning members of the mosque where one of the suspected Boston bombers attended services.
Tamerlan Tsarnaev, who was killed in a shoot-out with police on Friday, was still going to prayer services at a Cambridge, Massachusetts, mosque just weeks before the bombing.
Mosque spokesman Yusuf Vali said the 26-year-old had previously caused disturbances there, and imams had threatened to ban him following a confrontation during a prayer service.
Place of worship: A banner reading 'United We Stand For Peace on Earth' stands outside the Islamic Society of Boston mosque in Cambridge, Massachusetts, where Tamerlan Tsarnaev attended
Mr Vali told NBC News that as soon as they learned of Tamerlan's alleged involvement 'we immediately called law enforcement and said: "Listen, we've got folks who knew him and if you need any information, we're here."'
'Those folks have already met with the FBI,' he added.
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Tamerlan Tsarnaev was killed in a police shoot-out on Friday following a manhunt to track down those responsible for bomb attacks at the Boston Marathon finish line which killed three and injured a further 264.
His younger brother Dzhokhar Tsarnaev was tracked down and charged on Monday with using a weapon of mass destruction to kill. He could face the death penalty if convicted.
Suspects: Tamerlan Tsarnaev, left, was killed in a police shoot-out on Friday. His younger brother Dzokhar, right, was charged on Monday with using a weapon of mass destruction to kill and could face death if convicted
Family members have said that in recent years Tamerlan Tsarnaev had fallen under the influence of a new friend who steered the previously apathetic young man toward a strict strain of Islam.
Under the tutelage of a friend known to the Tsarnaev family only as Misha, Tamerlan gave up boxing, stopped studying music, and began a religious makeover, his family said.
This new-found radicalism came to a head at a Friday prayer service at the Islamic Society of Boston mosque in Cambridge three months ago.
Tamerlan was reportedly thrown out of the mosque after sparking a 'shouting match' with an imam who had held up assassinated civil rights leader Martin Luther King Jr as an example of a man to emulate.
He was eventually readmitted, but one member of the congregation, who gave his name only as Muhammad, told the LA Times: 'He had an anger inside ... I can’t explain what was in his mind'
The moment of the explosion at the Boston Marathon finish line: Three people were killed and a further 264 injured in the two blasts, which happened last Monday afternoon
Mr Vali, the mosque's spokesman, elaborated on the story. He said that as the imam had begun speaking of Dr King, Tamerlan stood out and accused the speaker of being a 'non-believer' and a 'hypocrite'.
'The congregation yelled back, "You need to leave",' Mr Vali said. 'And then the leadership had a conference with him and told him, that you need to stay silent or you are not welcome here.'
He eventually returned to the mosque, and continued to attend services there until recently.
No one has come forward to claim the body of Tamerlan Tsarnaev, it has been revealed, as investigators continue to piece together his movements prior to the attack