A detention officer who discovered a holster that had concealed a gun used to murder a police officer expressed his "astonishment" after colleagues missed it during a search, an inquest heard.
Richard Adams shouted "how the f*** did he get a loaded gun in a holster into custody?" after his Metropolitan Police colleague Matt Ratana was gunned down by Louis De Zoysa in a custody centre in Croydon, south London, on 25 September 2020.
De Zoysa had earlier been arrested and searched but officers failed to find the antique revolver the 26-year-old had in an underarm holster despite discovering bullets in his pocket.
Mr Adams also said "he's got a f****** holster on" after discovering it under De Zoysa's arm, an inquest at Croydon Town Hall heard on Tuesday.
Dominic Adamson KC, representing Sgt Ratana's partner, Su Bushby, asked the officer if this was him "expressing astonishment" that the firearm was not found.
Mr Adams replied: "Yes".
The officer told the inquest he felt "very uneasy" about De Zoysa once he arrived at the custody suite and noticed the detainee had an unusual walk.
He said: "As he was brought into custody he kept his back to the wall and took a sidestep so his back stayed against the wall."
After arriving at Croydon's Windmill Road custody centre, De Zoysa was allowed to walk without an officer gripping his arm, or handcuffs.
Mr Adams said colleagues should have held on to De Zoysa and that they were "outside the reactionary gap" because they walked more than an arm's length from the detainee.
Police sergeant Gavin Hutt, who drove De Zoysa to Windmill Road, agreed with Mr Adamson that he had not properly monitored the gunman as he left the custody van, and did not see that his hands were hidden under his jacket.
De Zoysa managed to move his handcuffed arms from behind his back to fire at Sgt Ratana.
The 54-year-old New Zealand-born officer, who had served in the Met for almost 30 years and was three months from retirement, was hit in the chest by the first of three shots discharged by De Zoysa within three seconds.
A second bullet struck him in the thigh before De Zoysa was wrestled to the ground by other officers, and a third round hit the cell wall.
Former tax office data analyst De Zoysa, who was living in a flat on a farm in Banstead, Surrey, discharged a fourth shot while on the cell floor, hitting an artery in his own neck and causing him brain damage.
He is serving a whole-life prison sentence for Sgt Ratana's murder after a trial earlier this year, during which his legal team argued that he was suffering an autistic meltdown at the time of the shooting.
The inquest also heard that since the shooting of Sgt Ratana, custody suite staff must wear body armour.
In a three-year period between 2018 and 2020, there were 296 instances of contraband being brought into custody suites, 29 of which were weapons, it was said.
The inquest continues.