They've become known as Black Hat and White Hat, two mysterious figures weaving through the Boston Marathon crowds, carrying instruments of death. One suspect is dead, one still at large. But who are they?
According to several law enforcement officials and the suspects' uncle, the two men are brothers.
The Associated Press identified suspect No. 2, in the white cap, as 19-year-old Dzhokhar A. Tsarnaev of Cambridge, Mass. A massive manhunt is underway in Watertown, Mass., to find him.
Suspect No. 1 was killed in a gun battle with police. The Associated Press identified him as 26-year-old Tamerlan Tsarnaev, Dzhokhar Tsarnaev's older brother.
Tamerlan Tsarnaev practiced martial arts and boxing, even aspiring to fight on the U.S. Olympic team. Dzhozkar Tsarnaev had been on the wrestling team at a prestigious high school and won a scholarship from the city to pursue higher education. Neighbors recalled the ethnic Chechen brothers, living on a quiet street in Cambridge, Mass., riding bikes and skateboards.
The brothers, who came from a Russian region near Chechnya, lived together on Norfolk Street in Cambridge. They had been in the country for about a decade, according to an uncle, Ruslan Tsarni of Montgomery Village, Md.
Less was immediately known about Tamerlan, believed to be 26 when he was killed overnight in a shootout. He was the stockier one identified in video released to the public, wearing a black baseball cap and khaki pants. He was involved in martial arts, and competed in boxing matches. According to a crime website he was once arrested for domestic assault on a girlfriend.
"I don't have a single American friend. I don't understand them." he was quoted as saying in a photo package that appeared in a Boston University student magazine in 2010.
He identified himself as a Muslim and said he did not drink or smoke: "God said no alcohol." He said he hoped to fight for the U.S. Olympic team and become a naturalized American. He said he was studying at Bunker Hill Community College to become an engineer.
Dzhokhar, 19, attended the prestigious Cambridge Rindge and Latin school, participating on the wrestling team. In May 2011, his senior year, he was awarded a $2,500 scholarship from the city to pursue higher education, according to a news release at the time. That scholarship was celebrated with a reception at city hall.
He attended the University of Massachusetts at Dartmouth, Mass., university officials said Friday.
Their uncle, Ruslan Tsarni of Montgomery Village, Md., told the media Friday morning that the brothers "were losers" who hated everyone. He said his family had nothing to do with the suspects when they were growing up and hadn't spoken to them since 2009.
"I say Dzhokhar, if you are alive, turn yourself in and ask for forgiveness," Tsarni said.
Their father, Anzor Tsarnaev, spoke with The Associated Press by telephone from the Russian city of Makhachkala on Friday. He described Dzhokhar Tsarnaev as a smart young man.
"My son is a true angel," the Anzor Tsarnaev said. "Dzhokhar is a second-year medical student in the U.S. He is such an intelligent boy. We expected him to come on holidays here."
Russia's North Caucasus region has been plagued by an Islamic insurgency stemming from separatist wars in Chechnya.