A man has been arrested in connection with the investigation into the murder of a Metropolitan Police sergeant, as tributes were paid to the "extraordinary" officer.
Sergeant Matt Ratana was shot by a handcuffed suspect in the early hours of Friday at a custody suite in Croydon.
A man was arrested at around 2am of Sunday in Norwich, Norfolk, on suspicion of supplying a firearm.
The suspect for the shooting remains in a critical condition in hospital and police said they have not yet been able to speak to him.
It comes as Sgt Ratana, 54, was remembered by friends and teammates at East Grinstead Rugby Club where he was head coach.
Officers investigating the murder of Sgt Matt Ratana in #Croydon continue to work around the clock as part of a detailed and thorough investigation. A man has been arrested in the early hours of 27 Sep on suspicion of supplying a firearm.https://t.co/QenAu4LQvf
— Croydon MPS (@MPSCroydon) September 27, 2020
Also on Sunday Met Commissioner Dame Cressida Dick paid tribute to him as an "extraordinary person" who was "very good at his job".
She spoke after a morning wreath-laying at the National Police Memorial in central London, which was also attended by Mayor of London Sadiq Khan and Home Secretary Priti Patel to mark National Police Memorial Day.
Dame Cressida said Sgt Ratana's death might give people an insight into the dangers and risks officers face.
She said: "If some good can come out of this terrible incident in which we have had one of our officers murdered, it would be that more people can understand a little bit about the challenges of police work and to see us police as who we are – human beings, going to work to help people, to support people and to protect people.
"Matt was the epitome of that."
Sgt Ratana, was originally from New Zealand and joined the Met in 1991. He leaves behind a partner and a grown-up son.
In East Grinstead, the club flag was flown alongside the New Zealand flag and an All Blacks rugby team flag to honour Sgt Ratana's roots.
Tributes were laid outside the clubhouse and two periods of silence – for junior and senior club members – were held in memory of a man described by assistant head coach Ryan Morlen as an "irreplaceable figure".
Pc Sarah D'Silva, a player with the club's women's team and also an officer at Croydon police station, laid a signed Metropolitan Police jacket alongside the other tributes.
The 26-year-old told the PA news agency: "I can't put into words how shocked I am and also the colleagues that are beside me in the blue-line family. It's a completely tragic event."
Searches in Pollards Hill, Norbury, where the suspect was initially arrested by officers for possession of ammunition and possession of class B drugs on Friday, have finished, police said.
Other searches are taking place at an address on Southbrook Road, also in Norbury, and at a second address on Park Road, Banstead in Surrey, as well as forensic examinations on the custody suite where the incident unfolded in Croydon Custody Centre at about 2.15am on Friday.
The Independent Office for Police Conduct (IOPC), which attended the scene after the shooting, said the murder suspect had been taken into the building and sat in a holding area in the custody suite, then opened fire while still in handcuffs as officers prepared to search him with a metal detector.
This National Police Memorial Day is particularly poignant as so many mourn the death of a family member, a friend and a colleague. #RIPMattRatana
— Metropolitan Police (@metpoliceuk) September 27, 2020
He had earlier been arrested following a stop and search, then handcuffed behind his back before being taken to the station in a police vehicle.
No police firearms were fired in the incident, and the case is not being treated as terror-related.
Sgt Ratana is the eighth police officer in the UK to be shot dead in the last 20 years and the first to be murdered by a firearm in the line of duty since Pcs Fiona Bone, 32, and Nicola Hughes, 23, in September 2012.
The Met sergeant is the 17th from the force to be killed by a firearm since the end of the Second World War, according to the National Police Memorial roll of honour.