Dion Thompson was the first Defendant indicted by the State’s Attorney’s Office’s newly created Cold Case Homicide Unit 

Baltimore (Md.) July 30, 2026 - Today, State’s Attorney Ivan J. Bates announced the conviction of Defendant Dion Thompson for the First-Degree Murder of DC Metropolitan Police Sgt. Tony Mason, Jr. The Defendant faces two life sentences plus 33 years of incarceration at sentencing on August 5, 2026. Cold Case Homicide Unit Chief Kurt Bjorklund prosecuted this case. 

“The loss of Sgt. Mason is still fresh in the hearts of his family and his brothers and sisters on the DC Metro Police force,” said State’s Attorney Ivan J. Bates. “I sincerely appreciate all the tireless work by Chief Kurt Bjorklund, BPD, the FBI, and ATF to pursue this prosecution relentlessly. Their perseverance has delivered justice for the Mason family. As the inaugural case that launched our office’s Cold Case Homicide Unit, this prosecution holds a special place in our hearts as ministers of justice.”

Thompson was convicted of First-Degree Murder, Conspiracy, and related charges for shooting Sgt. Mason while he was off duty in November of 2017 at the 2800 block of Elgin Avenue. Thompson was also convicted of the Attempted Second-Degree Murder of a non-fatal victim who was with Sgt. Mason in his vehicle.

“For nearly a decade, Sergeant Mason’s death has weighed heavily on his family, our Department, and the community he served. Throughout this long journey, our partners at the Baltimore Police Department, the FBI, the ATF, and the Baltimore City State’s Attorney’s Office never stopped pursuing answers. Their commitment brought us to this moment,” said Interim Chief of Police Jeffery W. Carroll. “We hope this verdict provides some measure of peace for everyone who continues to feel the weight of his loss.” 

Cold cases are generally defined as those unsolved criminal investigations that remain open pending the discovery of new evidence. These cases were not solved initially through traditional means; “fresh eyes” are often needed to review existing work and pursue different avenues. The goal of the cold case investigator is not always to solve the case but to push forward the investigation meaningfully; often, these incremental steps lead to more significant advancements.

“Sergeant Mason’s grieving loved ones, friends and colleagues have waited almost nine years for this day. Dion Thompson’s conviction guarantees a reckless killer remains locked up so he can no longer inflict violence in our community,” said FBI Baltimore Special Agent in Charge Jimmy Paul. “The diligent and coordinated investigation reflects our unwavering commitment to bringing justice for victims regardless of how long it takes and holding violent criminals accountable to the fullest extent of the law.” 

The Cold Case Unit works closely with the Baltimore Police Department’s existing Cold Case Unit to ensure these unique cases are investigated with greater coordination and specialization. 

“Our detectives never stop working to seek justice for victims and their families,” said Baltimore Police Commissioner Richard Worley. “I want to recognize Detective Beauregard and our Cold Case Unit for their dedication and persistence in this investigation. This conviction is the result of hard work and collaboration with our partners at the State’s Attorney’s Office, FBI, and ATF. Most importantly, this conviction brings justice to Sgt. Mason’s family and honors his memory and service.”

The charges against Mr. Thompson resulted from a thorough inter-agency investigation conducted by the Baltimore Police Department Homicide Section, the Federal Bureau of Investigation, and the Bureau of Alcohol, Firearms, and Tobacco. This is yet another example of an older case that benefited from focused attention and resources.

“This sentence proves that violence in Baltimore will not go unpunished,” said ATF Baltimore Special Agent in Charge Charles Doerrer. “When our law enforcement agencies come together to solve and prosecute a case like this, we show our grit and determination to find justice for victims and families.”

Charging documents for Dion Thompson are available here. Victim and witness identifying information has been redacted.