A detailed picture is emerging of the Boston Marathon bomber killed in a shootout with police.
Tamerlan Tsarnaev is the suspect in the dark hat in the surveillance video released by the FBI.
He was a 26-year-old boxing and martial arts expert who once dreamed of becoming an American citizen and representing the United States at the Olympics.
But his YouTube channel reveals a darker side, a series of disturbing videos showing terrorist training camps and Al-Qaeda propaganda.
One YouTube video appears to be Tamerlan speaking in Russian to his brother about a trip to Moscow. Tamerlan is reported to have made a mysterious trip to Russia in 2012.
Tamerlan and his brother Dzhokhar fled the war torn Russian Republic of Chechnya and sought asylum in the United States eight years ago.
The brothers have two sisters who live in the New York area.
“It's crazy. It's not possible. I can't believe it!” said Tamerrlan’s uncle, who revealed Tamerlan called him just yesterday for the first time in two years and said he wanted to heal a rift in the family. “Yesterday he called me and said forgive me."
Tamerlan enjoyed dressing in stylish clothes and drove a Mercedes, but he seems to have had problems adjusting to American life.
In a 2010 profile in a Boston University magazine headlined "Will Box For Passport", he said, "I don't have a single American friend. I don't understand them."
He described himself as a devout Muslim, stating "I'm very religious. God said no alcohol. There are no values anymore. People can't control themselves."
He boasted in 2010 that he had a girlfriend who was half Portuguese, half Italian. He said she converted to Islam, saying, “She's beautiful, man.”
Tamerlan was a three times New England boxing champion. In 2009, he represented team New England in the National Golden Gloves tournament in Salt Lake City but was defeated.
He was a regular at a Boston mixed martial art gym. His former boxing coach, John Curran, told ABC news he is stunned Tamerlan was involved in the massacre, saying, “He was a fine young man, very good athlete, very courteous, quiet and just a nice guy. I’m shocked beyond belief that he was involved in this.”
Tamerlan studied engineering for two years at Bunker Hill Community College in Boston. The college was used as a location for the movie Good Will Hunting.
Just last year, his 45-year-old mother was arrested for allegedly stealing $1,600 worth of clothes from a Lord & Taylor department store near Boston.
Ironically, it was the surveillance camera from a Lord & Taylor store in downtown Boston that captured him and his brother on video planting the bombs.
Terror experts say there are still unanswered questions about what drove these two young men to become terrorists.
Harvey Kushner, author of Encyclopedia Of Terrorism, asked, "Where did they get their training? Who inspired them? Are they card carrying members of a terrorist organization? This is very important for the authorities to know."