An aging and frail Korean War veteran is hoping a retiring Baltimore detective named “Mad Dog” can crack his brother’s unsolved 1981 murder before he dies.

Solving the case is Robert “Bobby” Thompson’s last wish.

“This is my last chance,” Thompson told the Baltimore Sun Saturday. “I’m 83. All my brothers are dead. I’m the only one who can do this because I’m the only one left.”

He is relying on ace homicide gumshoe Albert “Mad Dog” Marcus, 65, who hopes he can solve the case before he retires at the end of the year, capping a 40-year career fighting crime.

“Bringing closure to the families,” he told the paper. “That’s the satisfaction.”

Tommy Thompson, 51, met his killer in his van on his way home on July 27, 1981. The father of four was shot three times with a .22-caliber pistol. The van struck a fire hydrant and stopped. Witnesses saw a man jump out and flee on foot.

Thompson, who worked for the Social Security Administration, said his brother died the next day.

“Where this guy got in his van, I don’t know,” Thompson told the Sun. He said he wonders if his brother knew his killer.

Thompson said that in the weeks after the murder, he posted a $3,000 reward for information and then upped it to $5,000. There were no takers.

Marcus, who shows up at crime scenes in custom-made suits, a Fedora and a Fu Manchu mustache, admitted that solving the case is a long-shot. The case file is as thick as an old phone book. He plans to track down people who were interviewed after the murder to see if he can jog their memories.

“There’s a little old lady in every neighborhood and she sees a lot,” Marcus told the Sun. “You've got to find that little old lady.”