Musa Khadzhimuratov, a former Chechen separatist fighter, said he had a social relationship with Tamerlan Tsarnaev, one of the two bombing suspects, but they never talked about religion or politics, The New York Times reported Friday.
Tamerlan Tsarnaev, 26, was one of two bothers suspected of setting off two bombs at the marathon , killing three people and injuring more than 260. He was killed by police; his younger brother Dzhokhar Tsarnaev, 19, is in custody.
The FBI has questioned Khadzhimuratov, 36, more than a dozen times, searched his family's small apartment in Manchester, N.H., subjected him to a polygraph and took a DNA sample, the newspaper said.
After revealing a note left by bombing suspect Dzhokhar Tsarnaev inside the boat he hid in after a shootout with police, FBI director Robert S. Mueller III said Thursday evidence pointed to "homegrown violent extremists."
But interviews of Khadzhimuratov could be a result of what Mueller said are the FBI's "ongoing efforts to identify any others who may be responsible."
"We have nothing to hide," Khadzhimuratov said. "But they began very nice, saying they needed an expert on the North Caucasus. Now they treat me like a criminal. They push, push, push. They say, 'Where do you think he made the bomb? It took 12 seconds to go off -- how do you think they set off the bomb?' "