Police are “painstakingly” searching four crime scenes in connection with the killing of an officer, while the suspect – who was handcuffed at the time of the shooting – remains in a critical condition.

Sergeant Matiu Ratana died after a 23-year-old gunman opened fire at Croydon Custody Centre in south London in the early hours of Friday.

Giving an update on Saturday evening, deputy assistant commissioner Stuart Cundy said investigators have CCTV from the custody suite and bodyworn video from the officers.

The suspect has not been spoken to yet due to his condition, he added.

Everyone working on this investigation ... does so with a heavy heart but a determination to find justice for our colleague and his family

Speaking outside New Scotland Yard, he said there were four crime scenes which were being “painstakingly” searched.

He added: “We have recovered the gun from the custody suite where Matt was shot and that gun is being forensically examined.

“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.”

Searches are taking place at an address on Southbrook Road and an area of nearby London Road, both in Norbury, south-west London, an address on Park Road in Banstead, Surrey as well as the custody suite where the shooting happened.

Investigations are continuing into how the suspect, who had been detained in an area of London Road, Pollards Hill for possession of ammunition and possession of class B drugs, was able to access the weapon.

Police said forensic searches at all four locations will be “rigorous” and are expected to take days to be completed.

Deputy Assistant Commander Cundy, who is leading the investigation, said Friday was a “dark and sad day for the police family” and offered his thoughts to Sgt Ratana’s partner, family and colleagues.

He added: “Everyone working on this investigation, from the forensic specialists to the local officers holding the cordons, does so with a heavy heart but a determination to find justice for our colleague and his family.”

Tributes have poured in for the popular officer, who was also head coach at East Grinstead Rugby Club.

Earlier, a friend said the officer had moved into custody work because he thought it was safer as he approached retirement.

Sgt Ratana, known as Matt to family and friends, thought working in the custody suite was his “safest option” as he neared the end of his lengthy police career, friend Neil Donohue said.

He told BBC Breakfast: “He thought it was his safest option just to see him through to his retirement and no-one expected this to happen – certainly not within the police cells.”

He described the officer as “the most nicest, generous man you could meet”, and said he was “just a really genuinely nice guy”.

Sgt Ratana, 54, was originally from New Zealand and joined the force in 1991.

Met Commissioner Dame Cressida Dick described Sgt Ratana as a “talented police officer” and said he was “big in stature, big in heart, friendly, capable, a lovely man and highly respected by his colleagues”.

His partner’s sister told The Sun he was aware of the dangers of being a police officer but saw it as “all part of the job”.

Describing the news of his death as “devastating”, she told the newspaper: “He was dedicated to being a police officer and had almost 30 years of service.

“He knew the dangers of working in London but for him it was all part of the job.”

Sgt Ratana’s cousin Adrian Rurawhe, a politician in New Zealand, said his relative was a “natural-born leader”.

He told Stuff news website: “We’re all devastated that we’ve lost our cousin, but also to hear about the way he has been killed.

“He was awesome, very outgoing and a natural-born leader. Some people have to learn how to be a leader, but it just came naturally to him.”

The suspect also shot himself during the incident at about 2.15am on Friday and is in a critical but stable condition in hospital.

No police firearms were fired and the case is not being treated as terror-related.

He was not regarded a subject of interest by security services, the PA news agency understands, but reports suggest he may have previously been referred to the anti-extremism Prevent programme.

Following the shooting investigators from the Independent Office for Police Conduct (IOPC) watchdog attended the scene.

The suspect was arrested by regular officers following a stop and search, then handcuffed behind his back before being taken to the station in a police vehicle.

The IOPC said he was 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.

IOPC regional director Sal Naseem said: “It is at that 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.”

Leroy Logan, a former Met superintendent, said there were questions to be answered around the circumstances which led to the shooting.

“How did that person come to be in the station, whether it’s in the yard or the building itself, and be able to produce a weapon, whether it’s on them at the time?” he told BBC News.

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.