Photos from the gun battle.

A gun battle in a quiet area of Watertown tonight left one of two suspects dead, a police officer critically injured and residents being told to lock their doors and stay away from the fronts of their homes.

At 4 a.m., Boston Police Commissioner Ed Davis tweeted:

One suspect dead. One at large. Armed and dangerous. White hat suspect at large.

State Police linked the two to an armed robbery of a 7-Eleven in Central Square, the murder of an MIT police officer and a carjacking that ended in East Watertown with a gun battle between the two men and Watertown and MBTA police.

State Police said the suspects began tossing explosives at police in addition to shooting at them. One MBTA officer, Richard H. Donohue, received critical injuries and was rushed to Mt. Auburn Hospital.

Police from Boston, Cambridge and Newton rushed to the area north of the Watertown Mall when Watertown Police issued an urgent plea for help. They were quickly joined by FBI and ATF agents and State Police. Davis rushed to the scene as well.

Police say that after pumping several bullets into the MIT officer at the Stata Center, the two carjacked a Mercedes SUV and headed outbound on Memorial Drive - they stopped at a gas station to let the SUV's owner out.

One of the suspects, the Black Hat Guy, was nabbed by police after the gun battle, with serious injuries of his own. He was rushed to Beth Israel Hospital, where he was pronounced dead from multiple trauma, including from what appeared to be an explosive device - police said he had one strapped to his chest.

The second suspect took off on foot and police said he was armed with both an assault rifle and either grenades or IEDs.

Residents of the area were warned to lock their doors and stay away from the fronts of their houses. Police prepared to evacuate some residents due to the presence of explosives, some of which bomb squads planned to explode on purpose.

Jay Gates reports:

It woke my wife up, she woke me up. We then heard a few vehicles screaming down our street. We're on Cypress, which is parallel to Laurel, where Ch 7 reported as the location of the shootout. During this, my upstairs neighbor was standing at the end of our driveway, just watching everything. I yelled at him to get inside, Several officers ran towards him, guns drawn and made him put his hands up, and I didn't see what happened after that, I ran out of the room!

At 1:01 a.m., Jamie Erdahl at NESN tweeted: