Police: One Boston bombing suspect dead, another on the run

(CNN) -- Two men suspected in the Boston Marathon bombing that killed three people this week terrorized the area overnight. One is dead, but the other is on the loose, police say, and he's armed and dangerous.

Police pursued two men early Friday who shot a police officer to death, stole a vehicle and threw explosives at law officers pursuing them. Authorities believe they are the same two men sought in the marathon attacks.

One died of injuries suffered while battling police early Friday, and the other is on the run in a nearby suburb, authorities said.

Both men allegedly killed one police officer late Thursday, wounded another early Friday and used explosives against police pursuing them.

Marathon 'Suspect number 2'

Police believe the man at large is "suspect number 2" in Monday's bombing. Federal, state and local law officers are swarming through the Boston suburb of Watertown, going door-to-door to track him down, said transit police spokesman Paul MacMillan.

Police warned Watertown residents to lock their homes and stay away from their windows and doors.

A surveillance image of the fugitive resembles photos of one of the suspects sought for alleged involvement in the marathon attacks that killed three.

The image of the man with bushy, wavy black hair, a pronounced chin and nose, and a slight build matches photos circulated of the man in the white cap, carrying a backpack near the scene of Monday's bombing.

Due to the strong similarity of the two images, police believe the fugitive may be "suspect number 2" in the marathon terror attack, MacMillan said.

The other suspect was injured in a a shootout with transit police and pronounced dead at a local hospital, according to a statement from the Massachusetts district attorney.

Police believe he is suspect number 1 in the marathon attack.

Boston's public transit authority has sent city buses to Watertown to evacuate residents while bomb experts comb the surroundings for possible live explosives.