Inmate accused of 2017 cold case killing of off-duty DC cop on date: docs

Investigators believe they solved the “painful mystery” of who killed an off-duty Washington, DC, cop while he sat in his parked car with his date — a case that sat cold for nearly seven years.

Chronic thief Dion Thompson, 24, allegedly pulled the trigger on Sgt. Tony Anthony Mason Jr. and the woman in November 2017 out of paranoia that they “were there to either rob him or retaliate against him for all the robberies he was committing,” prosecutors alleged.

Thompson is accused of driving up next to the car, firing at the couple and fleeing.

Mason, 40, was killed in the ambush, but his date survived.

Thompson remained on the lam and the case unsolved until investigators received a tip in early 2023 that led them to the career criminal — who was already behind bars on unrelated gun and drug charges.

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“For far too long, the details surrounding Sgt. Mason’s tragic death have remained a painful mystery,” Metropolitan Police Department Chief Pamela A. Smith said Wednesday.

“This arrest is a testament to the dedication of our law enforcement community and the collaborative efforts between agencies. While we cannot erase the pain of loss or the memories of that day, we can take solace in the fact that the person responsible is being brought to justice.”

Thompson, who was 18 at the time of the killing, allegedly confided in the tipster that he killed someone in a parked car but had no idea who his victims were, according to the charging documents.

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He spotted the vehicle as he was leaving his friend’s grandmother’s house in Baltimore and immediately grew suspicious that it was tailing him, either to rob him or to get revenge for the string of robberies he committed.

That’s when Thompson allegedly fired at least 16 rounds at the car and ran away.

The couple had simply been talking, enjoying alcoholic drinks and listening to music, investigators said. They had been dating for just one month.

Thompson learned later from watching the news that the victim was an off-duty police officer, the witness told detectives.

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He allegedly ditched his car in Philadelphia the night of the shooting, but bragged to his brother that he had finally killed someone.

Mason — a 17-year veteran of Washington’s Metropolitan Police Department — was not wearing his uniform at the time he was killed. He was also unarmed at the time.

The charging documents reference two other people — “Man-Man” and “Chub” — who were allegedly involved in the shooting. One later died in a car crash. Officials said no one else has yet been charged in the case.

Tracking down Thompson was easy — he is serving time in federal prison on unrelated drug and gun charges.

The cracked case marks the first prosecution brought by Baltimore State’s Attorney Ivan Bates’s new cold case unit, prosecutors said.

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