The Metropolitan Police confirmed that a 23-year-old man was detained at the scene.
A police officer was shot dead in the early hours of Friday morning at a custody centre in Croydon, London, the Metropolitan Police has said.
In a statement, the police said that the officer was rushed to hospital after the shooting at Croydon Custody Centre in Windmill Lane. He later died of his injuries.
A 23-year-old man arrested at the scene also suffered a gunshot wound and is in a critical condition, it added. A murder inquiry has been launched.
Commissioner Cressida Dick said that the "shocking incident" had sent shockwaves throughout the Met: "Policing is a family, within London and nationally, and we will all deeply mourn our colleague."
“We are in the early stages of the investigation and are still working to establish the circumstances surrounding the incident and we will provide further updates when we have them."