A gunman has been found guilty of murdering a custody sergeant after smuggling a revolver into a police station and opening fire in a holding cell while still in handcuffs. Former tax office data analyst Louis De Zoysa claimed diminished responsibility, but was unanimously convicted after a jury decided that he pulled the antique weapon's trigger deliberately and did not suffer an autistic meltdown. A three-week trial at Northampton Crown Court was shown distressing video footage of New Zealand-born Met Police Sergeant Matt Ratana being hit in the chest by the first of three shots discharged by De Zoysa within three seconds. Sgt Ratana died of his injuries in hospital despite the efforts of medical staff. Report by Jonesia. Like us on Facebook at http://www.facebook.com/itn and follow us on Twitter at http://twitter.com/itn