A relentless killer laid in wait Monday evening for a cabbie’s passenger in Brooklyn and opened fire, nearly killing the terrified driver, then chased his quarry down the block and executed him in the street.

The gunman, armed with a high-caliber weapon, was waiting for the 21-year-old victim as his cab pulled up on Dean St. near Schenectady Ave. in Crown Heights about 6:10 p.m., police sources and the cab driver said.

The shooter fired at least eight bullets into the gunmetal blue Toyota Highlander, punching five holes into the rear door on the driver’s side and two more into the door’s window. Another bullet ripped through the roof.

“I just dropped him off and heard the shots. I saw the bullets go into his body,” said the rattled driver, Ibrhahim Jalloh. “I thought I was going to die. I don’t know the guy. I just picked him up.”

Injured, the victim ran east for almost a block on Dean St., but the shooter chased him down and shot him again in the chest, sources said.

Medics rushed him to Kings County Hospital, but he couldn’t be saved.

The driver was unhurt.

“He was lucky,” a police source at the scene said.

Police have not yet released the victim’s name.

A group of friends gathered at the scene about two hours later. “We’re going to miss him. He wasn’t looking for any trouble. He was a kid. Just a kid,” said one of the friends, who didn’t give his name.

Cops made no immediate arrest in the case.