From there, they forced the driver to take money out of an ATM, then let him go. But his cell phone remained in the car, allowing police to track the vehicle after he called in the crime by "pinging" it to get its location.
The vehicle was revealed to be heading towards Watertown. The brothers arrived on a quiet residential street, driving two separate cars, Deveau which were spotted by a police officer in his vehicle who notified the local station.
The officer was ordered to wait for backup before engaging the suspects. But before they could arrive, Deveau said the two suspects each got out of their cars and began shooting at the officer, causing him to frantically reverse his patrol car to get away from the close-range fire.
"The two brothers are shooting at my first police officer that's responded and now within seconds I have two or three other police officers that pull up," he said. "We had just finished shift so two off-duty officers on their way home heard the call. I have six police officers in this very tight area engaged in a gunfight. We estimate there [were] over 200 shots fired over a five to ten-minute period."
From there, the brothers began lighting improvised hand grenades -- "very rough devices," according to Deveau -- and threw a pressure cooker bomb similar to the ones used in the marathon attack that caused a "major explosion." None of the officers were killed and no bystanders were wounded during the fierce exchange, which Deveau attributed to their skill in handling the situation.
"My heart is out to the M.I.T. officer and his family, but how the Watertown police aren't attending a funeral of our own based on what happened on that street over that period of time is just talent, guts and glory that my officers did," Deveau said.
The fight ended when Tamerlan Tsarnaev, after leaving cover to close in on the officers while firing his weapon just "five to ten feet" away, ran out of ammunition. He was tackled by multiple officers and handcuffed.
In the confusion, Dzokhar Tsarnaev returned to the stolen car and made his escape -- apparently fatally wounding his sibling in the process.
"Here comes the black SUV, the carjacked car, directly at them," he said. "They dive out of the way and he runs [over] his brother and drags him a short distance down the street."
At the same time, officers rushed to attend to a transit cop who was seriously wounded after being hit in the groin by a bullet, giving Dzokhar Tsarnaev an opening to escape. Deveau said the officer had lost a lot of blood, "but we hope he can make a recovery."
Deveau also described the confrontation the next day, in which officers responding to a resident's report of blood in his backyard used heat sensing technology to locate the suspect hiding in a boat. According to Deveau, Tsarnaev exchanged fire with cops on scene. Devau's account is the first report that Tsarnaev participated in the gun battle himself.
"It was back and forth," he said."My understanding, yes -- he was firing."
He said that Tsarnaev emerged from the boat weak and in need of aid. Deveau said had no indication he was interviewed on scene by the police.
"My understanding is he didn't have anything to say," he said. "I don't know for sure."
Asked about Deveau's account, the FBI cautioned that only official information released by the FBI or the U.S. attorney should be considered accurate.
Additional reporting by Hunter Walker.