Police, FBI and SWAT teams are actively searching for suspect number two, who is on the run.
Boston Police have described the surviving bomb suspect, the man pictured in the white hat in FBI footage, as "terrorist".
Watertown Police, State police and the Boston police commissioner gave a very brief press conference in the early hours of this morning and gave the details of how suspect number one, who was pictured wearing sunglasses and a grey hoodie, was killed in a shootout in the residential suburb.
"We believe this is a terrorist, we believe this is a man that's come here to kill people," said Boston Police Commissioner Ed Davis. "We need to stop him."
A local police officer explained how the first suspect was killed at the press conference. "During the course of our pursuit, several explosive devices were discharged from the car at police officers," he said. "In the exchange of gunfire, one of the suspects we believel was struck and taken into police custody.
"One was able to escape and there is an active search by tactical teams.
"The most important that we are doing right now is for public safety and the safety of those people in that neighbourhood."
By Caitlin McBride in Boston