A former Metropolitan Police Department lieutenant has been arrested and charged with involuntary manslaughter after fatally shooting a D.C. Public Library police officer Thursday afternoon.

A police spokesperson identified the victim of the shooting as 25-year-old Maurica Manyan, a Maryland resident.

According to MPD, former Lieutenant Jesse Porter, 58, was leading a training session for D.C. library police officers on how to use extendable batons. Towards the end of the session, which was held at the Anacostia Neighborhood Library, Porter “fired a shot” that killed one of the trainees, D.C. police chief Robert Contee told reporters Thursday. Contee said the shooting took place in a training room in the lower level of the library, where about six people — including Porter, Manyan, and several other trainees — were present.

In interviews with police after the shooting, trainees said they believed it was an attempted joke gone tragically wrong, and that Porter did not realize he had a live weapon in his hands instead of a training gun.

Porter retired from MPD almost two years ago and was “acting in his personal capacity as a professional trainer” at the time, according to police. Contee said the library contracted with Porter to have him train the officers on how to use “ASP batons,” extendable batons that police and security officers use.

According to charging documents, Porter told police he was joking around with the class when he took his gun out of his holster and heard it go off. The documents state that Porter repeated over and over to a responding officer: “Why did I do this? Is she okay?”

The shooting happened as trainees were preparing to take a group photo at the end of the training, witnesses told police. The group was poking fun at Manyan for not being ready for the group photo when a gun went off, per charging documents. Witnesses said they believed Porter was “trying to be playful,” and that he thought he still had a training gun – a weapon with no live ammunition – in his holster.

Trainees said Porter had already pretended to shoot Manyan with a training gun once during the session, according to charging documents. They wondered if Porter was trying to make that same kind of joke again, not realizing he was holding an actual loaded gun.

Porter has been released as he awaits trial.

The D.C. Public Library hires its own police, separate from the Metropolitan Police Department. Its officers are licensed to be armed, DCPL spokesperson George Williams told the Washington Post. According to an open job posting, these employees patrol DCPL properties and ” respond in cases of criminal activity and violations of the DCPL behavioral guidelines.”

“It’s a very tragic situation that we’re dealing with here,” said Contee. “My condolences to the family of the deceased library police officer and to their entire agency.”

In a statement on Friday afternoon, DCPL said Manyan joined the team in February, and was known “for her bubbly, warm personality.”

“Our thoughts are with Maurica’s family, and the DCPL family, especially our colleagues in the Office of Public Safety, as we mourn the loss of Maurica together,” the statement continues. The library will be closed through Sunday as a result of the incident.

This post has been updated to include a statement from the D.C. Public Library and additional details from charging documents.