A St. Louis teen allegedly killed a mechanic who fixed his mom’s BMW — when the worker asked to be paid for the repairs, police said.

Isaiah Gholson, 17, is facing charges that include first-degree murder in the June 9 killing of 52-year-old mechanic Kerry Charley, who police say was shot after refusing to let Gholson and his mother, Ranada Anthony, take the luxury car home without paying for it, the St. Louis Post-Dispatch reports, citing court documents filed Tuesday.

Charley’s sister told the newspaper that the father of three was shot five times in the chest after repairing the car at his home, where police said they were able to match the mechanic’s records to find that the vehicle was registered to Anthony.

“He was a very, very generous person,” said Charley’s sister, who identified herself only as Cindy. “He was always willing to help someone in need when it came to their vehicles. He loved working on cars, it was like a passion for him.”

That enthusiasm for his craft, Charley’s sister said, led him to fix cars at much lower prices than typical repair shops.

He even allowed some customers to make good on their outstanding debts by paying in installments, she said.

But investigators said that didn’t happen this time, alleging that Gholson shot Charley as the mechanic stood by the driver’s window after the teen grabbed keys to the upscale ride and hopped inside, KMOV reports.

At the same time, Anthony, 39, started pushing and hitting Charley’s 32-year-old girlfriend, who was shot twice in the back by Gholson as she ran away. The woman was seriously injured but later identified Gholson as the shooter and Anthony as the woman who assaulted her, police said.

Both Gholson and Anthony, who was charged with assault, failure to report a crime and hindering prosecution, remain held without bond after a detention hearing Wednesday.

Neither of them reported the shooting to police and deny being at Charley’s home, despite records linking the vehicle to the mechanic, the Post-Dispatch reports.