Feds Look Into Accused Bomber's Dark Side

April 22, 2013— -- In the widening federal probe into the Boston Marathon bombing, authorities are uncovering growing evidence of 26-year-old Tamerlan Tsarnaev's violent dark side and increasing disaffection and disgust with things Christian and American.

Tsarnaev, the older of the two brothers accused of detonating explosives near the marathon finish line, died during a firefight with police early Friday morning.

Authorities are working to uncover the details of Tsarnaev's life in the hope their search will help provide a motive for the deadly bombing.

The FBI sought to question Tamerlan's American wife, Katherine Russell, who was seen over the weekend leaving Tsarnaev's Cambridge apartment with her three year old daughter. A Rhode Island native, she converted to Islam and changed her name from Katherine to Karima.

Her lawyer, Amato DeLuca told ABC News that Russell was shocked by recent events.

"She couldn't believe it," DeLuca said. "Imagine, just think of yourself. You got a brother or a father or somebody and you see their picture and it's like wow, what's going on. She was in complete shock."

DeLuca also said Russell works long hours as a health care aid and suspected nothing. She was at work when she heard about his involvement four days after the bombing. DeLuca wouldn't talk about the investigation or if his client has been questioned by the FBI.

Her family issued a statement saying: "In the aftermath of the Patriots' Day horror we know that we never really knew Tamerlane Tsarnaev. Our hearts are sickened by the knowledge of the horror he has inflicted."

Federal authorities also continued to search for more possible explosives. ATF agents searched behind a Cambridge rug store, in an area where the brothers' father used to repair cars.

Evidence of troubled moments in Tsarnaev's past turned up in police records, which showed that his then-girlfriend called 911 in tears to report that he was beating her up. And local prosecutors told ABC News that they are now exploring whether Tamerlan Tsarnaev had any connection to the brutal 2011 murder of three young men, one of whom was a friend and sparring partner.

The three were found with their throats slashed, covered in marijuana and cash.

Authorities are also looking closely at the six month trip Tsarnaev took last year to Russia and Chechnya, at a time that rebel groups there carried out a number of violent attacks. Just last year alone Dagestan lost 115 police officers in almost 300 terror attacks. Investigators want to know whether he met with any of the notoriously fierce extremists there.

Neighbors in Cambridge told ABC News that Tsarnaev was a changed man, swearing off tobacco and alcohol, linking to extremist jihadist videos, and saying, "I don't have a single American friend. I don't understand them." One neighbor said he expressed anger about America and Christianity.

"So with the Bible he believed that it was a cheap copy off the Koran and that it was used as an excuse for many wars fought by America to invade countries and take land away," said Elbrecht Ammon. "He mentioned how America is a colonial power and wants to take as much land as possible and most casualties are innocent people shot down by American soldiers."

Today, the mother of the two brothers, Zubeidat Tsarnaev, told ABC News today from Russia that Tamerlan was always the leader of her two boys, and that after the bombing he called her to say, "Everything is okay, thanks to Allah."