Jesse Hartnett, 33, was hit three times in the arm by a gunman dressed in several layers of clothing who tried to execute him, officers said.
"We have some video we captured of this. This is absolutely one of the scariest things I've ever seen," said police commissioner Richard Ross in the northeastern US city.
"This guy tried to execute the police officer. The police officer had no idea he was coming. It's amazing he's alive."
The officer, a veteran of five years on the force, returned fire and hit the suspect, who tried to flee on foot, but was quickly arrested.
Ross said the motive for the attack was unclear, but that the suspect, in his 30s, was dressed in several layers of clothing.
