Meanwhile, Watertown residents within the 20-block radius have been told to stay in their homes. They have also been told not to offer a lift to anyone in the streets in the vicinity.
According to Colonel Timothy Alben, head of Massachusetts state police, Suspect number 2 is "considered armed and extremely dangerous", , said. Davis had the following advice for Watertown residents: "Do not open your doors. Stay in your home. We believe this man to be a terrorist and we need to get him into custody."
Ed Davis, the police commissioner of Boston, confirmed that they were trying to apprehend a man identified on Thursday night as Suspect Two. He was captured in video footage released to the public carrying a black backpack amid the marathon crowd shortly before the bombings and wearing a white baseball cap.
Suspect 2 was believed to be hiding somewhere within the Watertown area, at the end of a dramatic police chase in which explosive devices were thrown out of a Mercedes SUV that had been car-jacked from MIT.
During the car chase, one of the two assailants - who police said was Suspect 1 from the marathon bombing photographs - was injured and later died at Beth Israel hospital.
Alben said Suspect 2 was dressed in a grey, hoodie-type sweatshirt. He is a light-skinned, Caucasian male with longer brown curly hair.