On September 25, 2020, Sgt Ratana, also known as Matt, 54, was shot in the chest while a handcuffed suspect was being taken into custody at Croydon Custody Centre.
Louis De Zoysa, of Banstead, Surrey, was shot in the neck during the altercation and was taken to the hospital.
Mr De Zoysa, 25, entered a not guilty plea via video connection at Northampton Crown Court.