A career criminal smiled on the witness stand yesterday, fondly recalling how he ripped off $4,000 from a suicidal Long Island man with empty promises to kill him.

Melvin Fleming, 55, recounted how he met motivational speaker Jeffrey Locker on July 11, 2009, on an East Harlem street when the stranger gave him $5 and made a shocking request.

“He was looking for someone to make him dead, to kill him,” said Fleming, now in a drug rehab program in Queens.

Despite a long rap sheet and admitted pot and heroine habits, Fleming said his moral code wouldn’t let him kill Locker.

“I couldn’t do anything like that,” he said. “I accepted a few bucks and kept moving.”

Locker was killed five days after he met Fleming. Kenneth Minor, 38, is on trial for the brutal slaying.