The suspects were identified by law enforcement officials and family members as Dzhokhar and Tamerlan Tsarnaev, brothers from a Russian region near Chechnya.
Tamerlan Tsarnaev, a 26-year-old who had been known to the FBI as Suspect No. 1 and was seen in surveillance footage in a black baseball cap, was killed overnight, officials said.
His brother, a 19-year-old college student who was dubbed Suspect No. 2, escaped. He was seen wearing a white, backward baseball cap in the images from Monday's deadly bombing at the marathon finish line.
"Dzhokhar, if you are alive, turn yourself in and ask for forgiveness," Tsarni said.
They lived near Boston and had been in the U.S. for about a decade, Tsarni said. He said he had not seen them since December 2005. He said his nephews had struggled to settle themselves in the U.S. and ended up "thereby just hating everyone."
Asked what he thought provoked the bombings, Tsarni said: "Being losers, hatred to those who were able to settle themselves. These are the only reasons I can imagine of. Anything else, anything else to do with religion, with Islam, it's a fraud, it's a fake."
Tsarni, who described himself as Muslim, said his brother left the U.S. and he had not talked to him since 2009. He said they had a personal falling out but did not elaborate.
Chechnya has been plagued by an Islamic insurgency that has carried out deadly bombings.
Tsarni said vehemently that Chechnya had nothing to do with the attack.
"I've been following from Day One, but would never imagine that somehow the children of my brother would be associated with that. So it is atrocity."