Black Hawk helicopters and heavily armed police descended on a Boston suburb yesterday in a massive search for an ethnic Chechen suspected in the Boston Marathon bombings, hours after his brother was killed by police in a late-night shootout.

The normally traffic-clogged streets of Boston were empty as the city went into virtual lockdown after a bloody night of shooting and explosions. Public transport was suspended, air space restricted and famous universities, including Harvard and MIT, closed after police ordered residents to remain at home.

Public transport suspended and air space is restricted

Officials identified the hunted man as Dzhokhar Tsarnaev, 19, and the dead suspect as his brother, Tamerlan Tsarnaev, 26, who was killed Thursday night in the working class suburb of Watertown.

Details emerged yesterday about the brothers, including their origins in the predominantly Muslim regions of Russia’s Caucasus, which have experienced two decades of violence since the fall of the Soviet Union. The fugitive described himself on a social network as a minority from a region that includes Chechnya, Dagestan and Ingushetia.

A man who said he was their uncle said the brothers came to the United States in the early 2000s and settled in the Cambridge, Massachusetts, area.

“I say what I think what’s behind it – being losers,” Ruslan Tsarni told reporters in suburban Washington. “Not being able to settle themselves and thereby hating everyone who did.”

Tsarni said he had not spoken to the brothers since 2009. He said Monday’s bombings on the finish line of the world-famous Boston Marathon that killed three people and injured 176 “put a shame on our family. It put a shame on the entire Chechen ethnicity.”

The bombing, described by President Barack Obama as “an act of terrorism,” was the worst such attack on US soil since the plane hijackings of Sept. 11, 2001.

The FBI said the twin blasts were caused by bombs in pressure cookers and carried in backpacks that were left near the marathon finish line as thousands of spectators gathered. Authorities cordoned off a section of the suburb of Watertown and told residents not to leave their homes or answer the door as officers in combat gear scoured a 20-block area for the missing man, who was described as armed and dangerous.

The manhunt had covered 60 per cent to 70 per cent of the search area by yesterday evening.