A police station detainee shot dead a custody sergeant while he was handcuffed, using an antique revolver he had hidden in an underarm holster, a murder trial has heard.

Northampton Crown Court was told that Met Police officer Matt Ratana was killed by one of four bullets fired by Louis De Zoysa, in an incident captured on CCTV at a custody block in Croydon, south London.

Opening the case against De Zoysa on Wednesday, prosecutor Duncan Penny KC said the 25-year-old had been taken to a holding cell after being found with seven rounds of ammunition in London Road, Norbury, south London, at night on September 25, 2020.

At the start of his opening speech, Mr Penny explained that he would be speaking in short sentences because of communication difficulties experienced by De Zoysa, who suffered brain damage after the fourth bullet struck him in the neck.

The prosecutor told the jury: “On Friday the 25th of September 2020, Louis De Zoysa shot dead Sergeant Matthew Ratana in a holding room.

“Louis De Zoysa pulled the trigger on purpose twice when he was pointing the gun at Sergeant Ratana.

“In total, the prosecution say Louis De Zoysa pulled the trigger on purpose four times.”

The jury was told De Zoysa, of Banstead, Surrey, was stopped by the police in Norbury, was searched by police officers on the street, put in handcuffs and found to be “carrying cannabis and seven rounds of ammunition”.

Mr Penny told the jury of seven men and five women: “The police officers did not find that Louis De Zoysa was carrying a loaded revolver in a holster.

“The gun and holster were probably concealed under one of his armpits.”

After his arrival at the custody facility in Windmill Road, Croydon, De Zoysa was was taken to a holding cell, the court heard.

“Louis De Zoysa kept the gun hidden,” Mr Penny said. “Louis De Zoysa was put in a holding room. Louis De Zoysa was still handcuffed.

“He was able to point the gun Sergeant Ratana. He deliberately shot Sergeant Ratana once to the chest, at very close range. He did not give a warning.”

Before showing the jury CCTV of De Zoysa’s movements before he was detained in Norbury, Mr Penny said other officers at the custody block “were not able to stop” De Zoysa, whose first bullet caused a fatal injury to the left lung and heart of Sgt Ratana.

Mr Penny said: “Three further shots were fired during the struggle with officers that followed. The prosecution say the second shot was another deliberate shot at Sergeant Ratana.

“The fourth shot caused severe and life-threatening injury to Louis De Zoysa.”

The defendant was 23 when the shooting happened and was living in a flat at a farm in Banstead, having bought the gun, which was legal to own due to its antique status, on the internet in June 2020.

Bullets of the correct calibre for the gun are no longer made, Mr Penny said, but De Zoysa “bought the parts to make the bullets” and made ammunition at the farm.

Mr Penny alleged: “Louis De Zoysa knew the gun worked with the bullets he had made.”

De Zoysa, who appeared in the dock in a wheelchair and with his right arm in a sling, denies murder.

The trial continues.