Video report by ITV News Correspondent Sejal Karia
A murder investigation is underway after a "long-serving" and "much-loved" police sergeant was gunned down as he was detaining a suspect at a custody centre in Croydon on Friday morning.
Metropolitan Police chief Cressida Dick said: "This morning, we learned of the shocking death of a much-loved colleague, a long-serving sergeant in the Metropolitan Police who was working last night in our Croydon custody suite.
"I have visited and spoken to our officer's partner, together with other colleagues, and we are of course giving her the best support we can. My heartfelt condolences go to her, to their family, to his colleagues and his close friends.
"I'm thinking also of everyone who was involved in and those affected by this terrible event. We are all deeply shocked and very sad.
"The Met is a family, policing is a family in London and across the United Kingdom. And today we police are all mourning a great loss."
What we know so far:
A long-serving Metropolitan Police sergeant was shot at the Croydon custody centre at approximately 2.15am on Friday.
London Ambulance Service administered CPR on the officer but he later died in hospital.
A 23-year-old man has been detained by officers in connection with the shooting.
The suspect is in a critical condition in hospital with a gunshot wound.
Met Commissioner Cressida Dick said indications were that the suspect shot himself.
The Metropolitan Police said no police firearms were discharged during the incident.
A murder investigation is underway and the incident has been referred to the Independent Office for Police Conduct.
Early indications suggest the suspect turned the gun on himself, Ms Dick said. The 23-year-old suspect remains in a critical condition in hospital.
"Early indications are that the suspect shot himself. This has not yet been established as a fact," Ms Dick said.
"The man, I can tell you, remains in a critical condition in hospital."
ITV News Correspondent Dan Rivers discusses the unanswered questions with the case
ITV News understands the suspect had been brought in to the custody suite and was being given a Covid test when he pulled out a gun, shooting the officer five times before turning the gun on himself.
In a statement on Twitter, the Prime Minister offered his "deepest condolences" to the family and friends of the police officer.
He said: "We owe a huge debt to those who risk their own lives to keep us safe."
The officer, believed to have been in his 40s, was given CPR at the scene in Windmill Lane, Croydon but died later in hospital, the Metropolitan Police said.
Police are in the process of informing all of the officer's family before they confirm his identity.
No police firearms were discharged during the incident, police said.
The Home Secretary has echoed the Prime Minister's words, Priti Patel said "I am deeply shocked and saddened by the tragic killing of the officer in Croydon".
Ms Patel continued: "This is a sad day for our country as, once again, we see the tragic killing of a police officer in the line of duty as they are trying to protect us and keep us safe."
ITV News Correspondent Sejal Karia was live at Croydon police station:
Just before 2pm on Friday, a dozen uniformed police officers silently walked to the custody centre and laid two large bouquets of flowers.
They bowed their heads as they stood side-by-side in tribute to their colleague. They left a minute later without saying a word.
A poem pinned to one of the bouquets read: “Time to come home dear brother, Your tour of duty through, You have given as much as anyone could be expected to do."
Metropolitan Police officer Stuart Hutson, who appears on the BBC One television programme The Met - Policing London said he was one of the officers to respond to the incident.
He joined other members of the police to change their social media profiles to black, with a blue line, as a mark of respect.
He said: "This morning my team and I responded to the worst possible radio transmission from custody, words and scenes I shall never forget.
"The unimaginable happened to our police family. We have lost not only a good skipper but also a real gentleman. One of the best. RIP brother."
Former police officer Joe Kennils described the victim as "kind-spirited" and "funny".
He said: "He was a new skipper, I was his new inspector. We gelled.
"He was funny, very funny. He was kind-spirited, thoughtful, generous, always hungry and could sleep standing up. He was a gentleman and I will truly miss him."
He added: "He could light up a room. Always laughing and always looked out for the younger cops. A gent."
Community police officer Jacqueline Kufuor burst into tears after laying flowers outside the centre in tribute to her colleague.
She told PA that the deceased officer was “a lovely guy” and “the nicest man I have ever met”.
She said: “You never expect this to happen when you go to work. For him to have been in custody and for this to have happened, it is just so sad.
“He was a very lovely man. He was such a nice man. When he sees you, he would just stand and talk to you. He would ask you about your job and how your are coping and how you are doing out there.
“So when I ever had issues, I would just talk to him.”
Members of the public have been turning up all day to hand over flowers at the centre and pay their respects.
A friend of the victim, who got to know him from playing rugby together, described him as an "inspiration".
“It is sad that our force are out in that position. They are just men and women doing a job," the man who would only give his name as Paul.
“They are at the front line and on the bad end of it but nobody deserves that.”
He added: “We all looked to him – on the field or off the rugby field, he always found a way to gee us up. Losing that is big.
“The man was a machine. He went from training with us last night to come to his shift work here in Croydon. He would do that week in and week out.
“He bought into the whole family atmosphere that we had at the club."
He said that some of his team mates are not sure how to take the news. He added that the officer was looking forward to retirement.
“I think he earned his stripes, if you ask me,” he added
Lissie Harper, the widow of Pc Andrew Harper who was killed on duty last year, said in a statement: “This is devastating news. No person should go to work never to return. No human being should be stripped of their life in a barbaric act of crime.
“Another hero has been taken from us in unwarranted violence.
“They protect us but who protects them? Another life is gone in a disgraceful act that reminds us of the danger our police officers face with every shift they begin.
“My heart is broken for yet another member of our blue line family, and all of his family, friends and colleagues who must now accept a life without him in it.
“My thoughts and love are resolutely with them.”
The officer is the 17th from the Met to be killed by a firearm since the end of the Second World War, according to the National Police Memorial roll of honour.
Former Met Police Chief Superintendent Dal Babu said: "When anything like this happens, and it happens very rarely, it devastates the whole police family. It is very upsetting and people will want to know why this happened, particularly as it happened in a police station."
Scotland’s First Minister, Nicola Sturgeon said: “I wanted to take the opportunity to convey my deepest condolences to all of the officer’s loved ones.
“This is a heartbreaking reminder of the danger police officers confront every single day on our behalf and of the enormous debt of gratitude we owe them as a result of that.”
Labour leader Sir Keir Starmer said in a statement on Twitter: "Horrific to hear of a police officer being shot and killed in Croydon.
"Our police put themselves in harm's way every day to keep us safe.
"All my thoughts are with the officer’s family, friends and colleagues."
Mayor of London Sadiq Khan said it was "heartbreaking" that a police officer lost his life in the city.
Addressing police officers, he said: "I want to thank you for the service you give in our city. Our city is united in having you in our thoughts and prayers."
Speaking outside New Scotland Yard, Mr Khan said: “That a police officer can be killed in a police station is a source of great concern, not just to police, not just to those of us politicians who are charged with giving the police the tools they need, but everyone.
“One of the reasons that this man was arrested is that the police are bearing down on people who want to commit acts of violence.
“It’s a source of not just huge regret and sorrow, but it is heartbreaking that this person has then gone on to kill this officer.”
He added: “The whole of London stands with the family and friends and police in London mourning the brutal killing of the police officer.
“I think his family and friends are in the thoughts and prayers of all Londoners now.
“I was really privileged to join the Commissioner, Home Secretary and police officers in the one-minute silence.
“We’re doing all we can to keep our brave police officers as safe as they possibly can be.
“Every time a police officer starts his or her shift, they start their shift knowing the risk to their personal safety and it is possible they can lose their life in the line of duty."
Ken Marsh, chairman of the Met Police Federation, which represents rank-and-file officers, said: “The murder of a colleague on duty is utterly devastating news.
“Officers across London are in shock and sick to their stomachs at the nature of his death.”
The National Police Chiefs’ Council tweeted: “There are no words to adequately describe this tragic and deeply upsetting event. Our sincere condolences go to the officer’s family, friends and wider @metpoliceuk colleagues. This is a sad day.”
Other police forces have tweeted messages of condolence to the Metropolitan Police:
Policing minister Kit Malthouse updated MPs about the officer’s death, adding: “May justice follow this heinous crime.”
Raising a point of order in the House of Commons, Mr Malthouse said: “We ask our police officers to do an extraordinary job.
“The fact that one of them has fallen in the line of performing that duty is a tragedy for the entire nation."
He added: “I know the entire House will offer their condolences to his family and friends and colleagues.
“May he rest in peace and may justice follow this heinous crime.”
Commons Speaker Sir Lindsay Hoyle added: “It is shocking news. This should never happen to the people that protect us and make us safe. All our thoughts and prayers go with the family and friends and the police community.”
Shadow justice secretary David Lammy said it was "appalling news".
He added: “It is tragic when an officer loses their life in the line of duty while doing their job keeping the public safe.
“My thoughts and condolences are with the officer’s family, colleagues and friends.”
Yvette Cooper, chair of the Commons Home Affairs Committee, said: "It is truly awful news that a brave police officer has been killed.
"My thoughts and deep sympathies go out to the family, friends and colleagues of this brave officer - and also to everyone in policing who will be feeling this loss deeply.
"Every day our police put themselves in harm's way to keep us all safe - it is devastating for this to happen to someone working to protect others."
John Apter, National Chair of the Police Federation of England and Wales said the news was "utterly devastating and heartbreaking".
He added: "Our thoughts are with the officer's family, friends and colleagues at this most terrible time.
"Policing is a family and when we lose one of our own in such a devastating way it effects us all. The dangers police officers face every day are very real and sadly, as we have seen can result in officers making the ultimate sacrifice."
Steve Reed, Labour MP for Croydon North, said his thoughts were with the officer’s family and colleagues.
He tweeted: “All of us in Croydon are in shock at this heartbreaking tragic news.
Croydon Central MP and shadow policing minister Sarah Jones said it was "shocking news".
Reverend Catherine Tucker, who went down to the centre to see if anyone needed prayer or support, said: “The action taken against the police is really unacceptable but I also feel sorry for the perpetrator.
“Sadly, I am not surprised there has been a shooting in Croydon.”
Rev Tucker, who is of the Holy Church Croydon parish, which includes the centre in its catchment area, described the region as having a diverse community who live in a highly-deprived setting.
She said: “There are tensions between the police and young people particularly in relation to stop and search and the way the police relate to the community.”
Najma Ali, who lives opposite the police station said that the incident was "scary".
"I've lived here for 12 years in this area and nothing like that has happened before," she said.
Local resident Wilhemina Dew, 45, was on the school run when she noticed there was a lot of police around and heard about the shooting.
She said: “It makes me feel scared.
“Whatever the reason, whatever the tensions, shooting the police is unacceptable because we all need to feel safe.”
The incident has been referred to the Independent Office for Police Conduct who will lead an independent investigation.