Teen suspect in Baltimore killing of DC officer was ‘paranoid' about being targeted, tipster said

More than six years after an off-duty D.C. police officer was shot and killed as he sat in a car in Baltimore, a suspect has been charged.

Sgt. Tony Mason Jr. died after he was shot in west Baltimore in 2017. He was 40 and had served on the Metropolitan Police Department for 17 years.

Baltimore officials announced Wednesday that Dion Thompson, now 24, was charged in Mason’s murder after a cold case investigation in collaboration with federal officials. Thompson was 18 at the time of the crime.

According to new information provided by a tipster, Thompson, an alleged drug dealer, was in the area when he saw a parked car with two people inside, the tipster told police.

He “became paranoid” and believed the people in the car were there to “either rob him or retaliate against him for all the robberies he was committing,” court documents say. He picked up two friends and opened fire on the car.

Mason was shot and killed. A woman he had dated for about a month was shot and wounded.

An exhaustive investigation found that neither Mason nor the woman were involved in any criminal activity or gang activity, court documents say, and there’s no indication that Thompson knew Mason was an officer.

Police found 16 shell casings on the scene, shot from two 9 mm pistols.

At a news conference Wednesday, D.C. Chief of Police Pamela Smith thanked investigators for their determination.

"For far too long, the details surrounding Sergeant Mason's tragic death have remained a painful mystery. However, the Baltimore Police Department, the FBI, the ATF, and the Baltimore City State’s Attorney’s office never stopped following up on tips and tracking down leads," she said.

Thompson already was in federal prison on drug charges. A lawyer representing him in that case told the Associated Press he is not representing him in the murder case, which wasn't listed yet in online records.

A car pulls up and someone opens fire

Court documents give accounts of what happened the day Mason was killed.

The woman who survived the shooting told investigators that she and Mason had been sitting in a black Nissan Versa in the 2800 block of Elgin Avenue after midnight on Nov. 4, 2017. They were talking, drinking and listening to music, court documents say.

A dark-colored car pulled up next to them and a passenger called out “Yo” or “Hey, y’all,” the woman recalled.

Then at least one person inside that car began shooting and sped off.

Mason and the woman were both shot. Mason was hit in the left side and left arm, and was pronounced dead less than two hours later, court documents say. The woman was shot in the leg and survived.

‘I got one tonight, dummy’

The tipster who contacted police say Thompson described what happened. He said he was with two friends at the house of one friend’s grandmother.

When Thompson left the house, he said he became paranoid when he saw two people in a parked car. He thought they were a threat to him. He contacted his friends, told them to get guns, went back to pick them up and committed the crime, the tipster said.

Thompson said he dropped off his two friends and went home to ask his brother for more bullets. His brother said he was tired of wasting bullets on him because Thompson hadn’t killed anyone yet.

“I got one tonight, dummy. Watch the news,” Thompson said that he replied.

Thompson learned later, from watching the news, that he had killed an off-duty officer and injured a woman, the tipster said.

He went to Philadelphia to get rid of the car used in the crime, he said.

One of the friends who Thompson was with has since died; the other has not been charged.

Four months later, Thompson was arrested in a drug raid in which fentanyl, cocaine, marijuana, a gun and more than $10,000 cash were found, court documents say.

Investigators seized electronic devices and found that Thompson directed people to the area of the killing. Text and call logs appeared to have been deleted from several devices.

Federal prison records say Thompson is set to be released in January 2026.

Mason had been on non-contact status with the Metropolitan Police Department because of an "internal investigation," a police spokesman said.

Investigators offered a reward of $60,000 for tips on Mason’s murder. The tipster has never asked to receive the reward, court documents say.

Baltimore prosecutors said the case will be handled through a new cold case unit, demonstrating a commitment to finding justice no matter how long ago crimes occurred.

Stay with NBC Washington for more details on this developing story.