(NBC NEWS) Boston and its suburbs, universities and transit system were on total lockdown Friday as police hunted for marathon bombing suspect Dzhokhar Tsarnaev -- on the loose after his accomplice brother was killed in a stunning chain of events that left one cop dead and another injured, officials said.
During a desperate effort to flee after their photos were released by the FBI, the brothers carjacked a Mercedes SUV and told the driver they were the men behind Monday's double-blast attack at the race and had just killed a campus security officer, a source told NBC News. The driver was released unhurt.
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The older brother, Tamerlan Tsarnaev, was killed after a wild chase and firefight, but Dzhokhar was still at large in a densely populated area, and an associate was being sought. Adding to the nightmare, an explosive was found in Boston Friday morning and disabled, an official said.