A jury has retired to consider its verdict on a gunman accused of murdering a Metropolitan Police sergeant using an antique revolver smuggled into a south London custody centre.

Lawyers acting for Louis De Zoysa, who claims he did not mean to shoot Sgt Matt Ratana, have argued the 25-year-old has a partial defence of diminished responsibility due to an “autistic meltdown”.

Jurors at Northampton Crown Court have been told Sgt Ratana, 54, died of a chest wound after being hit by two bullets at Croydon’s Windmill Road custody block in the early hours of September 25 2020.

De Zoysa, from Banstead, Surrey, denies committing murder while he was handcuffed in a holding room, after being found with bullets by members of a street patrol.

Addressing the jury before it retired on Thursday, Imran Khan KC, defending, asked its members to consider the evidence by stepping into De Zoysa’s shoes.

“Look at it not from your point of view as neurotypical individuals… but from his,” Mr Khan said.

The defence lawyer said of CCTV footage of the fatal shooting: “All this beggars belief, you may think.

“Out of the blue, without a hint of provocation, the gun was fired.

“The thought might be going through your head: ‘what the hell just happened and why did it happen?’

“The events cry out for an explanation because when you look at it, there appears to be no logical, rational, sane explanation for what you are seeing. The prosecution has not provided an explanation.

“What it shows is a young man completely out of control, out of his mind.

“Anything else simply doesn’t make sense. Louis was someone experiencing a meltdown.”

The alternative to the defence’s suggested scenario, Mr Khan said, was the proposition that an autistic young man, surrounded by three police officers in a cell, was intent on murder in the middle of the night.

“If he was intent on murder how was he going to escape? It simply doesn’t make any sense,” Mr Khan said.

Before the jury retired at 2.02pm, Mr Justice Johnson urged the panel of seven men and five women not to feel under any time pressure to reach a verdict.