MIT said right after the 10:30 p.m. shooting that police were sweeping the campus in Cambridge and urged people to remain indoors. They urged people urged to stay away from the Stata Center, a mixed-use building with faculty offices, classrooms and a common area.
The suspects' images were released hours after President Barack Obama and first lady Michelle Obama attended an interfaith service in Boston to remember the dead and the wounded.
At the Cathedral of the Holy Cross, Obama saluted the resolve of the people of Boston and mocked the bombers as "these small, stunted individuals who would destroy instead of build and think somehow that makes them important."
"We will find you," he warned.
In the past, insurgents from Chechnya and neighboring restive provinces in the Caucasus have been involved in terror attacks in Moscow and other places in Russia.
Those raids included a raid in Moscow in October 2002 in which a group of Chechen militants took 800 people hostage and held them for two days before special forces stormed the building, killing all 41 Chechen hostage-takers. Also killed were 129 hostages, mostly from effects of narcotic gas Russian forces used to subdue the attackers.
Chechen insurgents also launched a 2004 hostage-taking raid in the southern Russian town of Beslan, where they took hundreds of hostages. The siege ended in a bloodbath two days later, with more than 330 people, about half of them children, killed.
Insurgents from Chechnya and other regions also have launched a long series of bombings in Moscow and other cities in Russia. An explosion at the international arrivals hall at Moscow's Domodedovo airport in January 2011 killed at least 31 people and wounded more than 140.