ST. LOUIS – A St. Louis police officer was charged with fatally shooting his coworker while the two were "playing with firearms" Thursday morning.

Nathaniel Hendren was charged Friday with involuntary manslaughter and armed criminal action in 24-year-old Katlyn Alix's death. His mugshot was released on Monday.

READ: St. Louis police officer shot by on-duty officer with a gun not issued by the department

According to a probable cause statement, Hendren met Alix at his apartment in the 700 block of Dover Thursday morning. Hendren was on-duty at the time and Alix was not.

While at his apartment, both officers were playing with guns when Hendren took out a revolver. Hendren emptied the cylinder of the revolver and put one cartridge back in it.  

Nathaniel Hendren
St. Louis police officer Nathaniel Hendren was charged in Katlyn Alix's death.
Photo provided by Hendren's friend

WATCH: Friends call officer Hendren a good guy

He spun the cylinder, pointed the gun away and pulled the trigger. The gun didn’t fire. Then, Alix took the gun and pointed it at Hendren and pulled the trigger, it didn’t fire then either.

Hendren took back the gun, pointed it at Alix and pulled the trigger. But this time, the gun fired, hitting Alix in the chest. She was taken to the hospital where she later died.

WATCH: Circuit Attorney Kim Gardner gives statement on charges filed in the death of Katlyn Alix

According to the statement, another on-duty officer, Hendren’s partner, was at the apartment at the time of the incident.       

He said he felt uncomfortable with the situation and didn’t want any part of it and started to leave. As he was leaving the apartment, he heard a shot. He went back into the room and saw what happened, according to the statement.

READ: 'We want answers': Colleagues remember slain St. Louis police officer

A GoFundMe was set up to pay for Alix's memorial. In just hours, the campaign garnered more than $5,000, which was its goal. Click here if you'd like to donate.

Visitation for Alix will be held Tuesday from 1 to 9 p.m. at Kutis Funeral Home on Gravois Road. Wednesday, there will be a prayer service at the funeral home at 9:15 a.m. that will be followed by a 10 a.m. mass at the Cathedral Basilica.