The bombings on Monday killed three people and wounded more than 180 others, tearing off limbs in a spray of shrapnel and instantly raising the specter of another terrorist attack on U.S. soil.
Chechnya is the home of an Islamic insurgency that has carried out deadly bombings in Russia and the region, but its militants have never been known to export violence to the West.
Investigators in the Boston case have shed no light on the motive for the bombing and have said it is unclear whether it was the work of domestic or international terrorists or someone else entirely with an unknown agenda.
As officers fanned out across the Boston area, Bryce Acosta, 24, came out of his Cambridge home with his hands up.
"I had like 30 FBI guys come storm my house with assault rifles," he said. They yelled, "Is anybody in there?" and began searching his house and an adjacent shed, leaving after about 10 minutes.
The endgame — at least for Suspect No. 1 — came just hours after the FBI released photos and video of the two young men at the finish line and appealed to the public for help in identifying and capturing them.
State Police spokesman Dave Procopio said police realized they were dealing with the bombing suspects based what the two men told a carjacking victim during their getaway attempt overnight.
Tsarni, the men's uncle, told The Associated Press that the brothers traveled here together from Russia. He called his nephews "losers" and said they had struggled to settle themselves in the U.S. and ended up "thereby just hating everyone."
Tamerlan Tsarnaev had studied accounting as a part-time student at Bunker Hill Community College in Boston for three semesters from 2006 to 2008, the school said.
Dzhokhar Tsarnaev was registered as a student at the University of Massachusetts Dartmouth, the school said. The campus closed down along with colleges around the Boston area.