Boston on Lock Down as Manhunt Continues for Dzhokhar Tsarnaev - NBC Right Now/KNDO/KNDU Tri-Cities, Yakima, WA |

Boston on Lock Down as Manhunt Continues for Dzhokhar Tsarnaev

Posted: Updated:

(NBC News) One became an American citizen last year on Sept. 11. The other was a boxer who once said: "I like the USA."

The two known suspects in the attack on the Boston Marathon - one killed, one on the loose - are brothers with a background in the separatist Russian republic of Chechnya, law enforcement officials told NBC News.

The suspect at large early Friday was Dzhokhar Tsarnaev, 19, born in Kyrgyzstan, who became a naturalized American citizen on Sept. 11, 2012, according to documents obtained by NBC News. He had a Massachusetts driver's license and was living in the Boston suburb of Cambridge. He was the suspect in the white hat in surveillance photos from the marathon released by the FBI, authorities said.

Authorities were hunting him door-to-door in the Boston suburbs, and more than 1 million people were ordered to stay indoors in a lockdown that paralyzed the region.

His brother, Tamerlan Tsarnaev, was killed overnight after an extraordinary crime spree: The brothers shot and killed a college security officer, carjacked an SUV and hurled explosives as police in Watertown, Mass., authorities said.