With Boston virtually paralyzed, thousands of officers with rifles and armored vehicles swarmed the streets in and around the city on Friday, hunting for a 19-year-old college student wanted in the Boston Marathon bombing after his older brother and alleged accomplice was killed in a furious getaway attempt overnight.

 

During the long night of violence, the brothers killed an MIT police officer, severely wounded another lawman and hurled explosives at police in a car chase and gun battle, authorities said.

The suspects were identified by law enforcement officials and family members as Dzhokhar and Tamerlan Tsarnaev, ethnic Chechen brothers who had lived in Dagestan, which neighbors Chechnya in southern Russia. They had been in the U.S. for about a decade, an uncle said, and were believed to be living in Cambridge, Mass.