Tributes have been pouring in for Sergeant Matiu Ratana, the UK police officer shot dead in the early hours of Friday by a man in police custody in South London. The suspect is believed to have shot himself after shooting the officer in the chest at a Croydon custody center.

Sergeant Ratana was treated at the police station by fellow officers and paramedics but died later in hospital. A 23-year-old man was detained by officers at the scene and taken to hospital with a gunshot wound. He was reported to be in a critical condition.  

The London Metropolitan Police said no police firearm was discharged during the incident and a murder investigation had been launched into the death of the officer.  

The Independent Office for Police Conduct (IOPC) will conduct a separate independent investigation but has already said that the suspect had his hands handcuffed behind him when he fired the shots.

"What we have established is that the man was arrested for possession of Class B drugs with intent to supply and possession of ammunition," the IOPC  said in a statement on its website.   

"The man was handcuffed to the rear before being transported to Croydon Custody Suite in a police vehicle where he was escorted into the building. He remained handcuffed to the rear and seated in a holding area in the custody suite.

"His handcuffs remained in place while officers prepared to search him using a metal detector.   It is at the point that shots were fired resulting in the fatal injuries to the officer and critical injuries to the man. A non-police issue firearm, which appears to be a revolver has been recovered from the scene. Further ballistic work will be required."

London Metropolitan Police commissioner Cressida Dick said: "This is a truly shocking incident in which one of our colleagues has lost his life in the most tragic circumstances.

"My heart goes out to his family, direct colleagues and friends."

A lovely man 

Sergeant Ratana, known as Matt, had served with the Metropolitan Police for 29 years. 

Originally from Hawkes Bay, New Zealand, Ratana came to the UK in 1989 before joining the police two years later. He later returned for a short time to work in Auckland's police force. 

Dick said Ratana was a "much-loved officer":  "A lovely man, respected by his colleagues, officers, staff and of course by members of the public, including, I may say, suspects arrested or dealt with in custody,"

"He had a fantastic career, he gave 29 years of his life to the public of London; he has now tragically been killed on duty. His service will never be forgotten and we are deeply grateful for it and it is a really distinguished service from a lovely, lovely, much respected police officer," She added. 

Meanwhile New Zealand Prime Minister Jacinda Ardem said she was "incredibly sad"

"Sergeant Ratana worked in Auckland City and Counties Manukau until 2008, before returning to the UK. To all Matiu's whanau across the world, we share your sorrow and have all our condolences." She added.

He leaves behind a partner and an adult son from a previous relationship. 

The suspect was arrested by regular patrolling officers, in the Pollards Hill district, South London, for possession of ammunition and suspected possession with intent to supply Class B drugs, Dick confirmed. He remains in a critical but stable condition in hospital.

"This terrible incident underlines again how police officers face danger every single day, 24/7, 365 days a year, in their work to protect our public." Dick said. 

London mayor Sadiq Khan said he was 'devastated' by the death of Ratana who had "paid the ultimate price for helping to keep Londoners safe."

"They are the very best of us, and I remain in close contact with the Commissioner to offer her and the Met my ongoing support," Khan told reporters.

UK prime minister Boris Johnson tweeted: "My deepest condolences go to the family, friends and colleagues of the police officer who was killed in Croydon last night. We owe a huge debt to those who risk their own lives to keep us safe."