WATERTOWN, Mass. (AP) -- The two suspects in the Boston Marathon bombing killed an MIT police officer and hurled explosives at police in a car chase and gun battle overnight that left one of them dead and his brother on the loose, authorities said Friday as thousands of officers swarmed the streets in a manhunt that all but paralyzed the Boston area.

The suspects were identified by law enforcement officials and a family member as Dzhokhar and Tamerlan Tsarnaev, brothers from a Russian region near Chechnya, which has been plagued by an Islamic insurgency that has carried out deadly bombings. They lived near Boston and had been in the U.S. for about a decade, an uncle said.

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 19-year-old brother - dubbed Suspect No. 2 and seen wearing a white, backward baseball cap in the images from Monday's deadly bombing at the marathon finish line - escaped.

The law enforcement officials spoke on condition of anonymity because of the sensitivity of the unfolding case.