An eagle-eyed Good Samaritan helped cops bust a career criminal who allegedly had a high-powered assault rifle, after spotting what looked like a gun sticking out of the man’s backpack, police said.

Jamain Rattary, 36, was busted near his Bronx home July 31 for criminal possession of a loaded gun, among other charges.

Rattary had a Kriss Vector .45 caliber rifle, claim cops, who tweeted a photo Friday of the gun, complete with a scope and silencer.

Police said they also recovered a loaded magazine, a second extended magazine and more loose ammunition after a search warrant was obtained for Rattary’s apartment.

Rattary was charged in June with obstruction of governmental administration after he allegedly refused to get in a police car following a dispute with his mother.

The recidivist has at least 16 prior busts, including a 2008 attempted murder rap where a man was shot standing on a Bronx sidewalk. It’s unclear if that victim was an intended target.

Rattary is being held on $50,000 bail and is due in court Sept. 16.