The suspect in the murder of a police officer in south London is Louis De Zoysa, the BBC has been told.
New Zealand-born Sgt Matiu Ratana, 54, died in hospital after being shot at the Croydon custody centre as a handcuffed suspect was taken into custody on Friday morning.
Mr De Zoysa, 23, from Norbury, who is thought to have shot himself, is critically ill in hospital.
Another man has been arrested on suspicion of supplying a firearm.
Officers made the arrest at about 02:00 BST in Norwich. The man is currently in custody.
Police have not been able to speak to the man suspected of shooting Sgt Ratana.
He had initially been arrested for an alleged drugs offence and possession of ammunition.
The shots were fired as officers prepared to search the suspect - who was still handcuffed - with a metal detector, according to watchdog the Independent Office for Police Conduct (IOPC).
The second arrest came as Sgt Ratana was remembered by friends and teammates at East Grinstead Rugby Club, where he was head coach.
The West Sussex club's vice chairman Matt Marriot said they had to arrange two separate minute's silences because the "interest has been pretty enormous", with "people coming from all over the country".
He said Sgt Ratana, who was known as Matt, had been "a role model, a mentor and often a father figure", and the club mourned him "as a family member".
PC Sarah D'Silva, who plays for the club's women's team as well as working at Croydon Police Station, said it felt "extremely poignant" joining the minute's silence.
She wore her police uniform to pay her respects to Sgt Ratana, who she described as "an absolutely fantastic character, full of life, with the biggest smile you've ever seen".
Met Police Commissioner Dame Cressida Dick, speaking at the National Police Memorial in central London earlier, said she "hadn't been surprised at all" by the number of tributes paid to him.
"Matt was an extraordinary person... he had a wonderful personality and he was very good at his job," she said, adding that he was a "proud Kiwi".
Prince Charles also paid tribute to Sgt Ratana during a National Police Memorial Day service, saying his death was the "latest heartbreaking evidence of the risks".
Officers have been focused on four crime scenes in London and Surrey as part of the investigation, including the house where Mr De Zoysa's parents live.
Searches continue at Croydon Custody Centre, where the shooting happened, an address in Park Road, Banstead, Surrey, and an address in Southbrook Road, Norbury.
The search of another scene in Pollards Hill, where the suspect was initially arrested, has ended and cordons have been removed.
Residents near one of the search areas, in Banstead, Surrey, reported hearing a loud noise on Saturday morning, and were later told a controlled explosion had taken place.
The Banstead address is down a long driveway and its land contains a series of concrete bunkers. A marked police car has been guarding the entrance to the property.
Sgt Ratana was shot in the chest at Croydon Custody Centre at about 02:15 BST on Friday.
On Saturday evening, Deputy Assistant Commissioner Stuart Cundy said police had "recovered the gun from the custody suite where Matt was shot".
"We also have CCTV from that custody suite which shows the events, and we have body-worn video of our police officers who were involved in the circumstances surrounding the arrest of the suspect," he added.
The murder investigation is expected to focus on the motive for the killing.
The force has previously said the shooting was not terror-related.
It is believed the suspect was known to counter-terrorism police and his background may feature prominently in police inquiries, BBC home affairs correspondent Danny Shaw said.
The suspect had been referred to the government's Prevent programme, aimed at stopping people joining extremist groups and carrying out terrorist activities.
Sgt Ratana came to the UK in his early 20s in 1989 and joined the Met Police two years later.
He was originally from the Hawke's Bay area of New Zealand and was educated at Palmerston North Boys' High School, north of the capital, Wellington.
The officer, who had a partner and an adult son from a previous relationship, would have been eligible for retirement in two months.
Neil Donohue, who was a friend of the officer and runs a gym he used to attend, said Sgt Ratana had gone into "the custody side [of policing] purely because he had had enough out on the streets and he thought it was his safest option, just to see him through to his retirement".