A 25-year-old man has been convicted of killing a police sergeant with a hidden gun in a cell.

Louis De Zoysa shot Sgt Matt Ratana, 54, in the chest at a Croydon custody block in September 2020. He had been arrested with bullets by a street patrol and handcuffed in a holding room.

He fired four shots in total, injuring himself and Ratana, who died at the scene.

De Zoysa, a former tax office worker from Surrey, claimed he had not intended to shoot Ratana and that he had autism that affected his behaviour.

But a doctor and a prosecutor said he had acted deliberately and had control over his actions.

The jury at Northampton crown court found him guilty of murder after five hours.

De Zoysa nodded when he heard the verdict.

The verdict was heard by Ratana’s partner, Su Bushby, and the Met’s commissioner Sir Mark Rowley. Bushby said she still grieved for her “gentle giant” who would never be forgotten.

The judge thanked the jury for its public duty and said De Zoysa faced more charges for firearms and ammunition. He did not speak to De Zoysa, who had brain damage from shooting himself, and sent him to custody.

Ratana was a veteran officer from New Zealand who was close to retirement.

The IOPC said all forces should use metal detectors to stop similar killings. The police chiefs agreed and the Met had already started the scheme.

Cundy said De Zoysa was the only one responsible for Ratana’s death.