New Baltimore cold case unit identifies suspect in 2017 murder of off-duty DC Metro officer

BALTIMORE -- Dion Thompson has been charged with the 2017 murder of off-duty DC Metro Police Sgt. Tony Mason Jr. in Baltimore, State's Attorney Ivan Bates announced Wednesday.

It is the first case that the State's Attorney Office's new Cold Case Unit has prosecuted.

"A cold case is still very much fresh in the hearts and minds of the victim's family," Bates said. "My main job as State's Attorney is holding offenders accountable, bringing closure for those impacted, and ensuring justice for Baltimore, the victims, and their loved ones."

Mason was shot and killed in his vehicle while he was parked just after 12:30 a.m. on November 4, 2017, near the 2800 block of Elgin Avenue. 

According to charging documents, Mason and a woman, who authorities say was his girlfriend, were sitting inside a car across from the Elgin Townhomes apartment complex when a dark-colored car pulled up beside them. A passenger in the car called out "Yo" or "Hey Y'all," before one of the passengers opened fire. 

When police responded to the scene, they found Mason unresponsive in the driver's seat, suffering from "multiple gunshot wounds," documents say. The woman who was in the car with Mason suffered a gunshot wound to the leg.

According to the charging documents, Mason was unarmed, not in uniform, and not involved in any gang or criminal activity.

It was the same weekend that community activists had called for a ceasefire in Baltimore City.   

In a multi-agency investigation, the FBI and ATF announced a $60,000 reward for information leading to the arrest of the suspected killer in November 2018. The witness, to date, has not asked to be compensated, according to charging documents.

In early 2023, Metro Crime Stoppers received a tip from an individual who told police they were close with Thompson, who allegedly confided to him, admitting his involvement in Mason's murder. 

Thompson allegedly told the witness he did not know who was sitting in the car - but assumed that the occupants were there to retaliate against him for robberies he had committed.

Police said Thompson had been known as the leader of a drug organization called The Slickest Ones, operating in the Elgin Avenue area of Baltimore.

Thompson has been charged with first-degree murder, conspiracy, and other related charges, and is currently serving time in federal prison in New Jersey. He is currently serving time in federal prison in New Jersey for unrelated drug and weapons charges, including possession with the intent to distribute fentanyl and possession of a firearm in a drug trafficking crime.

The new Cold Case Unit will work with the Baltimore Police Department to emphasize existing unsolved investigations. 

Baltimore Police Commissioner Richard Worley said he hopes working with the new Cold Case Unit will help move cold cases forward. 

"By partnering with the State's Attorney's Office Cold Case Unit, we can work toward the shared goal of moving cases forward and bringing closure to victims' families. This should also put the perpetrators of these crimes on notice: You will get caught, and you will be held to account," Worley said.

Prosecutors say there were two other men in the car and at least one of them also shot at Mason.

One of those men, identified as Jerard Walker, died in a car accident in 2018. Police have not said if he was the one who shot at Mason.