The Tsarnaev brothers were pictured firing at police in the gunfight that occured outside the suburban Watertown home of Andrew Kitzenberg.
Mr Kitzenberg heard gunshots on the street and was able to capture the ensuing violence on his phone camera, which he then uploaded to Twitter and his own blog OnHand.
His photographs show a pressure-cooker bomb the brothers detonated on the street as well as the felled body of Tamerlan Tsarnaev.
The US authorities have confirmed that nearly 300 people were injured in the Boston Marathon bombings.
Official sources quoted by US media said the surviving suspect, 19-year-old Dzhokhar Tsarnaev, who is facing the death penalty after being charged for using a weapon of mass destruction, had indicated to interrogators that he and his 26-year-old brother, Tamerlan, had acted alone.