Jurors have been allowed to fire the gun that was allegedly used to kill a Metropolitan Police officer at a custody centre in south London.
Sergeant Matt Ratana, 54, was fatally shot in Croydon on 25 September 2020.
Louis De Zoysa, 25, is accused of murdering the officer using an antique revolver while being handcuffed.
The prosecution alleges De Zoysa “pulled the trigger on purpose four times” while he was handcuffed in a holding room at the custody centre.
The first two shots hit Sergeant Ratana, the third struck a wall during a struggle with officers, and a fourth hit De Zoysa in the neck.
On the second day of De Zoysa’s trial at Northampton Crown Court, a ballistics expert showed the jury how the revolver worked.
Anthony Miller, a forensic scientist, explained the gun was loaded with dummy bullets made of plastic and that it was completely safe to be used in the courtroom.
Members of the jury aimed the weapon at the ceiling while it was being fired.
Mr Miller told the court he had examined the gun and the ammunition that was recovered after the incident.
Asked by prosecutor Duncan Penny KC if the gun went off by accident during his rigorous testing, Mr Miller said it did not.
He added: “I dropped it on the ground, I struck it with a cloth-faced hammer and I generally treated it roughly.”
Defendant suffered brain damage
De Zoysa, who the court was told suffered brain damage as a result of the incident, sat in the dock in a wheelchair.
He was accompanied by an intermediary to help him follow the trial.
He had been arrested in Norbury, south London, during the early hours of 25 September 2020 after a police stop and search.
Officers found he had cannabis and seven rounds of ammunition.
But they failed to find the loaded revolver, which was in a holster.
The prosecution says it was “probably concealed under one of his armpits”.
After his arrest, he was handcuffed in the back of a police van and taken to the custody centre.
De Zoysa has denied murder.
His barrister told the jury on Wednesday that he was suffering an autistic meltdown at the time of the shooting.
The trial continues.