The manhunt included an army of federal, state and local police officers, assisted by the tactical presence of SWAT teams, K-9 dogs, armored vehicles and helicopters.
Tamerian Tsarnaev, the older brother, died of multiple gunshot and shrapnel wounds in the earlier shootout. His brother eluded capture by fleeing the nighttime gunfight in a car, running over his brother's limp body on the ground in the process. Police said he later abandoned the car and fled on foot.
Alben said the brothers exchanged over 200 rounds with the police during the shootout, and left seven explosive devices at the scene. The gunfight lit up the nighttime sky with sights and sounds of a war zone.
"We believe this is to be a terrorist," said Boston Police Commissioner Edward Davis. "We believe this to be a man here to kill people."
Officials said Dzhokhar Tsarnaev is a student at the University of Massachusetts in Darmouth 40 miles south of Boston and a native of the Chechen region of Russia who became a naturalized U.S. citizen in September of last year.
He and his older brother were identified Thursday afternoon in FBI video and photos as suspects in Monday's marathon blasts that killed three and injured 176. Both moved to the United States a decade ago with their parents.
The massive manhunt was launched by two hours of violent events, starting Thursday at 10 p.m. in Cambridge, across the Charles River from Boston. Police responding to a 7-11 convenience store robbery in Kendall Square discovered an MIT campus police officer shot to death in his cruiser. A short time later, a Mercedes SUV carjacking nearby resulted in police pursuit and a shoot-out with the marathon bombing suspects in Watertown on the western edge of Boston.
Officials said the suspects threw grenade-like bombs and fired guns at police during and after the chase. A transit policeman helping with the pursuit was seriously wounded. Officers shot Tamerlan Tsarnaev, the older of the two brothers, when he rushed toward them firing a gun. He was later found to have a small bomb strapped to his body. Emergency room doctors said he died from bullet and shrapnel wounds.