Davonte Washington, 15, of Northeast, was shot on a platform at the Deanwood Metro station at about 4 p.m. Saturday.

WASHINGTON — A 17-year-old has been arrested in the fatal shooting of a 15-year-old on a Metro platform last week.

Davonte Washington, 15, of Northeast, was shot on a platform at the station at about 4 p.m. Saturday. The police say Washington was involved in a conversation that escalated into an argument. He died later at a hospital.

Metropolitan Police Chief Cathy Lanier said at a news conference Tuesday that they would seek to charge the 17-year-old as an adult, and that charges would include second-degree murder. The suspect will be in court Tuesday afternoon, she said.

The arrest was made on Monday afternoon in Southwest D.C., Lanier said.

At the time of the shooting, a D.C. police commander said that the shooting didn’t appear to be random.

Lanier on Tuesday said that “it appears that there’s just no reason for” the shooting and that there was “no information that there was any acquaintance” between Washington and the suspect, but at the same time, “I don’t know that I would say [it was] completely random.”

She said more information, including a potential motive, would be available after the court proceedings Tuesday afternoon.

Both Lanier and Chief Ron Pavlik of the Metro Transit police said that security cameras on the platform were instrumental in identifying the suspect.

“Everywhere you go in that system, there is some video,” Lanier said.

An affidavit filed by the police describes what the footage shows.

Washington, his mother and siblings went into the Metro station and went to a farecard machine. As they were there, the suspect, part of a group of several people, walked past Washington and his family, not interacting with them.

Washington and his family then went to the platform and sat at one of the benches to wait for a train. A couple of minutes later, the suspect and his group walked past the bench, and the suspect looked at the bench, where Washington sat with his head down. “However, it appears as if one of [Washington’s] juvenile siblings was looking back at the suspect.”

The suspect then walked back toward the bench, pulling a gun from his waistband.

Washington stood up and walked toward the suspect, the affidavit continues. Witness statements in the affidavit say that the two had a brief conversation. One said that the suspect said, “What the [expletive] you keep looking at me for, you know me from somewhere?” Another witness said that one of the people the suspect was with told the suspect to “chill.”

The suspect had been carrying a white plastic bag, which the affidavit says contained takeout food. After the shooting, he handed it to one of the two people he was with and ran off, keeping the gun with him. Washington’s mother ran after him, shouting, “Stop him! He just shot my son!”

Pavlik said that almost all of several recent “high-profile events” on Metro have been closed, thanks to the use of security footage. He said that footage hadn’t been released to the public in an effort to get information, as often happens in such cases, because in this case it wasn’t necessary.

“We’ve got very good video,” Lanier said.

Washington was with his mother and siblings when he was shot. He was a student at Largo High School, in Upper Marlboro, NBC Washington reports, adding that he was in the Air Force JROTC program there. His family told NBC Washington that he was on his way to get a haircut for Easter.

WTOP’s Neal Augenstein contributed to this report.