A gun fanatic is facing a life sentence for the murder of a Met Police custody sergeant after smuggling a revolver into a holding cell and shooting him in the chest and thigh without warning.
Jurors who convicted Louis De Zoysa on Friday were shown distressing CCTV footage of the 25-year-old using a legally-bought revolver to gun down Sgt Matt Ratana in a holding cell at a police station in Croydon, south London, in 2020.
The jury panel, which took around five hours to unanimously convict the former tax office data analyst, were not told that a shortened infantry rifle, numerous types of ammunition, a pipe gun, and a dummy launcher were found at his rented property after the killing.
De Zoysa claimed diminished responsibility during a three-week trial, but was found guilty after a jury decided the cannabis user pulled the antique weapon's trigger deliberately and did not suffer an autistic meltdown.
Northampton Crown Court was shown slow-motion video of New Zealand-born Sgt Ratana being hit in the chest by the first of three shots discharged by De Zoysa within three seconds.
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.
Sgt Ratana died of his injuries in hospital despite the efforts of medical staff.
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 killer, 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 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 incident.
De Zoysa nodded twice as the judge confirmed with him that he had heard the guilty 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 De Zoysa was convicted.
Reading a statement outside court, Ms Bushby paid an emotional tribute to Sgt Ratana.
She said: "Today is about justice for Matt. His life was taken too soon in the line of duty doing a job that he loved - a cruel end to a lifetime of service and dedication protecting others.
"Whilst the court case has concluded, the constant feeling of grief and loss continues.
"My love for Matt, my gentle giant, will never end. He will never be forgotten."
Standing alongside Ms Bushby and her family liaison officer, Sir Mark said: "I first met Su in my first week as Commissioner when I visited Croydon to pay my respects to Matt on the anniversary of his murder.
"I'm inspired by the strength she showed then and more so by the strength she shows here today.
"I cannot begin to imagine how difficult this has been for her and for all of Matt's family and friends."
After the verdict, 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 immediately before he remanded him in custody.
The court was told that 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 to test that it worked.
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 a rifle was among items found at his flat and workshop in Banstead.
An examination of his digital devices confirmed his interest in weapons and uncovered material relating to ideologies including right-wing extremism, Islamic extremism and homophobia, all of which he later denied being interested in.
The Independent Office for Police Conduct (IOPC) said an investigation into the shooting found the officers who initially searched De Zoysa would benefit from more training, but commended them for their incredible bravery in trying to disarm him.
IOPC director of operations Amanda Rowe said: "Searching officers can request the removal of outer clothing, but it is not mandated by the legislation, policy or guidance.
"Given that we now know De Zoysa wore a gun holster beneath his coat, it is possible the search would have yielded different results if the coat was removed.
"The same officers should be commended for their incredible bravery in trying to disarm De Zoysa after he produced the firearm. They acted without hesitation, despite the significant danger they were placed in at the time."