The death of a young St. Louis police officer during a game of Russian roulette was a “tragic accident,” according to the lawyer for the cop charged in her killing.

Officer Nathaniel Hendren, 29, sported a black eye in his mugshot released Monday, when he was booked into jail for allegedly shooting his colleague Katlyn Alix.

Hendren injured himself by headbutting and breaking a back window of a police SUV following the fatal shooting Thursday night, sources told the St. Louis Post-Dispatch. Police took him into custody Monday in his room at St. Louis University Hospital, where he’d been hospitalized.

He is charged with involuntary manslaughter and armed criminal action.

“The death of Officer Katlyn Alix was a tragic accident that has unalterably impacted the lives of everyone involved,” said Hendren’s lawyer, Talmage Newton IV, in a statement. “I urge the public, as well as members of the police department, to wait until the investigation is complete, and all of the facts have been presented, before coming to any conclusions about what they believe happened that unfortunate morning.”

Police said Hendren and his partner, also 29, were on duty when they and Alix gathered at Hendren’s home. Just before 1 a.m., Hendren emptied all the bullets from his revolver and put one back in. He spun the cylinder, pointed the gun away and squeezed the trigger, but the gun didn’t fire, according to court documents.

Alix, 24, who was off duty, then took a turn, pointing the gun at Hendren and pulling the trigger. Then Hendren took the gun back and did the same — but this time it fired and Alix was struck in the chest.

Hendren and his partner called in the shooting on their police radios as they rushed Alix, a two-year veteran, to St. Louis University Hospital. She was pronounced dead at 1:07 a.m.

Hendren, who has been on the force for one year, is being held on $50,000 cash-only bail.

At a court hearing Monday morning, Hendren’s attorney requested a bail reduction that would let him free after posting 10 percent. A judge will rule later this week.

Both Hendren and his partner were placed on paid administrative leave by the department following the shooting — but Hendren was suspended without pay on Monday. The partner has about two years on the force.

It’s unclear how long the two were at Hendren’s home that evening. Some patrol cars are outfitted with GPS technology, but it’s unclear whether their car had it.

An autopsy is being performed, but toxicology results could take 12 to 16 weeks to complete.

Alix was married to another St. Louis police officer in October. Her husband was not at Hendren’s home when she was shot, sources told the Post-Dispatch.