A gunman has been found guilty of murdering a custody sergeant after smuggling a revolver into a police station and opening fire in a holding cell while still in handcuffs.

Former tax office data analyst Louis De Zoysa claimed diminished responsibility, but was unanimously convicted after a jury decided that he pulled the antique weapon’s trigger deliberately and did not suffer an autistic meltdown.

A three-week trial at Northampton Crown Court was shown distressing video footage of New Zealand-born Met Police Sergeant Matt Ratana being hit in the chest by the first of three shots discharged by De Zoysa within three seconds.

Sgt Ratana died of his injuries in hospital despite the efforts of medical staff.

Louis de Zoysa court case
Sergeant Matt Ratana (Metropolitan Police/PA)

A second bullet struck the 54-year-old in the thigh, before De Zoysa was wrestled to the ground by other officers as a third round hit the cell wall at Croydon’s Windmill Road custody centre.

De Zoysa, who was living in Banstead, Surrey, discharged a fourth shot while on the cell floor 16 seconds later, hitting an artery in his own neck and causing brain damage.

The 25-year-old, who now uses a wheelchair, has communication difficulties and is being treated at a healthcare unit in Northamptonshire, was arrested in London Road, Norbury, in the early hours of Friday September 25 2020.

A bag containing seven bullets and cannabis were found during a search of De Zoysa’s clothing and body, but officers did not discover a .41-calibre revolver loaded with six rounds.

During the trial, prosecutors said De Zoysa “retrieved” the weapon from a holster under his left arm, while handcuffed to the rear, as he was being transported to Windmill Road in a police van.

CCTV evidence suggested he managed to get hold of the gun with his right hand around 16 minutes before the shooting and then took advantage of a vent at the back of his overcoat to hide the weapon until the shooting.

Jurors deliberated for just over five hours over two days before unanimously convicting De Zoysa, who listened to the verdict sitting in a wheelchair in the secure glass-fronted dock.

Louis De Zoysa
Louis De Zoysa in the cell where he later opened fire (Metropolitan Police/PA)

De Zoysa nodded twice as the judge confirmed with him that he had heard the verdict being announced by the jury foreman.

Sgt Ratana’s partner, Su Bushby, and Metropolitan Police Commissioner Sir Mark Rowley were among those in the public gallery as the verdict was returned.

After the verdict, trial judge Mr Justice Johnson thanked the jury for its deliberations on the case and said it had “fulfilled an onerous but critically important public duty”.

Prosecutor Duncan Penny KC told the court that further firearms and ammunition charges faced by De Zoysa will be allowed to lie on the file at a sentencing hearing at the same court next month.

The judge did not address any remarks directly to De Zoysa, who has communication difficulties due to brain damage from a self-inflicted gunshot wound, immediately before he remanded him in custody.

After buying the antique revolver, which was legal to own, on the internet three months before the murder, De Zoysa used bullets he had made and tested that it worked, the court heard.

At the time of his arrest De Zoysa was travelling in the general direction of his father’s home in south-east London, having caught two buses and walked to the junction of London Road and Pollards Hill North.

Pre-trial hearings, at which De Zoysa was twice ruled fit to plead to the charges despite his communication problems, were told that an infantry rifle was among items found at his flat and workshop in Banstead.

Jurors were not told about the other weapons owned by De Zoysa, which also included a pipe gun, a dummy launcher and various types of ammunition.

An examination of his digital devices confirmed his interest in weapons as well as violence across a range of ideologies including right-wing extremism, Islamic extremism and homophobia.