Police are continuing to search farmland in Surrey which is believed to be connected to the murder of Sgt Matiu Ratana.
Five police vehicles were seen at the site in Park Road, Banstead, on Monday.
New Zealand-born Sgt Ratana, 54, died in hospital after being shot by a handcuffed suspect who was taken into custody in Croydon on Friday morning.
Louis De Zoysa, 23, from Norbury, who is thought to have also shot himself, remains critically ill in hospital.
A man was also arrested in Norwich on suspicion of supplying a firearm on Sunday. He remains in custody at a South London police station.
The BBC’s Daniel De Simone previously said the Banstead address is down a long driveway and its land contains a series of concrete bunkers.
controlled explosion took place at the site over the weekend and a marked police car had been guarding the entrance to the property.
BBC Home Affairs correspondent, Danny Shaw:
The murder inquiry appears to be expanding, with the former Ministry of Defence weapons depot in Banstead the focus of activity.
The site, disguised as a chicken farm during the war, is believed to be the last remaining ammunition depot to serve London during the Second World War.
Searches and forensic work can take a long time, but the presence of so many police officers and vehicles three days after the shooting suggests there may have been a significant discovery, or at least the prospect of one.
Detectives will want to find out why the shooting took place, whether it was premeditated and if other attacks were being planned.
Were other people involved or aware of what was going on?
At the same time, the Independent Office for Police Conduct has stepped up its own investigation, taking accounts from officers who were involved on the day of the shooting.
Police confirmed the other scenes undergoing searches are Croydon Custody Centre, where the shooting occurred, an area of London Road in Pollards Hill, where the suspect was initially arrested, and an address in Southbrook Road, Norbury.
On Monday, a video produced by community leaders in Croydon in tribute to Mr Ratana was shared on social media.
Posting a link to the footage on Twitter, Supt Andy Brittain said: “Matt touched the lives of so many,” while colleagues using the Met Police’s Croydon account called the video a “beautiful tribute to our incredible Sergeant”.
Supt Brittain, who covered Sgt Ratana’s shift on Sunday, also tweeted a picture of a McDonald’s breakfast, along with an All Blacks rugby shirt placed in the empty chair of Sgt Ratana.
Met Commissioner Dame Cressida Dick described the 54-year-old as “talented officer” who was “big in heart”.
MPs are due to hold a one minute silence for Sgt Ratana in the Commons later.
The Independent Office for Police Conduct (IOPC) said Mr De Zoysa was arrested on suspicion of possession of Class B drugs with intent to supply and possession of ammunition.
The IOPC confirmed he was handcuffed with his hands behind his back and had been taken to the custody centre in a police vehicle, before being escorted into the building.
The shots were fired as officers prepared to search the suspect with a metal detector, the IOPC said.
“A non-police issue firearm, which appears to be a revolver, has been recovered from the scene. Further ballistic work will be required,” said regional director Sal Naseem.
Sgt Ratana joined the Met in 1991, having moved to the UK in 1989.
He was originally from the Hawke’s Bay area of New Zealand and was educated at Palmerston North Boy’s High School’s, a town north of the capital, Wellington.
The Met said a murder investigation was under way, but the shooting was not being treated as a counter-terrorism incident.