An "inside agent" may have been involved in the audacious jewel and cash heist at a safety deposit vault in central London, a former armed robbery detective said on 13 April.

Thieves used heavy cutting equipment to get into the vault at Hatton Garden Safe Deposit between 2 and 5 April, breaking into 60 to 70 boxes. London's Metropolitan Police said.

Jim Dixie, a former detective for the Metropolitan Police's armed robbery and other armed crime unit, known as the Flying Squad, said he believed the criminals received help to break into the vault.

"[I believe] there was an inside agent who probably gave them a plan of the building, facilitated their entry perhaps and at the very least sold the information about the vaults or was probably on the job with them," he said.

Businesses in Hatton Garden, home to almost 300 diamond, gold and gem dealers and more than 50 shops, were closed over the Easter holidays when the robbery took place.

On 11 April, the Metropolitan Police released CCTV images of three suspects, showing them using a side door of the building.

In a statement released on its website, the police called the heist "highly audacious" and said the men entered and left the building several times.

It added a total of 72 safety deposit boxes were opened, out of 999 boxes in the vault. Seven of these were vacant.

In the same statement, it confirmed police received an alarm call in the early hours of 3 April from a company monitoring the building's alarms, saying an intruder alarm had been triggered.

The call was recorded and transferred to the police's Computer Aided Despatch system. A grade was applied to the call that meant no police response was deemed to be required. It said the police were investigating why this grade was applied to the call.

Dixie also said an underground fire in nearby central London's Holborn, which started in 1 April and burned for 36 hours, could have helped the thieves as it affected electric circuits in central London.

He said: "I'm not saying the suspects had anything to do with it but it must have been a godsend to them because it clearly disrupted the electrics and maybe the alarm systems in the area."

More about the Hatton Garden robbery