LONDON (AP) — Police said Friday a man has been arrested on suspicion of murdering an officer inside a police station in south London in September.

Sgt. Matiu Ratana, 54, was shot at Croydon Custody Center just after 2 a.m. on Sept. 25 by a handcuffed suspect. The suspect, who had been arrested for a separate offence, then appears to have turned the gun on himself.

Ratana, a hugely popular officer, was taken to hospital but later died from his wounds.

The 23-year-old man detained in connection with the shooting was in critical condition in a hospital with a gunshot wound.

London's Metropolitan Police said the man’s condition has since “stabilized” and is “no longer considered life-threatening." Police said the man was considered fit to be arrested on suspicion of murder on Friday.

The man remains hospitalized and officers will liaise with medical and legal teams in assessing when he will be fit to be questioned, police said.

It is rare for police officers to be shot and killed in the U.K., which has strict firearms laws. The officer is the 17th from the London force to be killed by a firearm since 1945.

Before Ratana, the last London police officer killed in the line of duty was Constable Keith Palmer, who was stabbed to death in March 2017 during a vehicle and knife attack outside Parliament.