Scotland Yard released images of men they are keen to question about the heist
A possible link between the "audacious" Hatton Garden heist and a nearby tool theft is being investigated.
City of London Police told the BBC it looked into the theft of Hilti DD350 drills in December in Fetter Lane. The case was closed without any arrests.
The force said it had passed the information to The Met, who confirmed the same model was used on the Hatton Garden Safe Deposit Ltd on 2 April.
Detectives are now investigating whether it was the same drill.
Thieves break into liftshaft, disable the lift, and abseil or climb down to basement
They use tools, including an angle grinder and crowbars, to force through shutter doors
Using a powerful drill, they then cut through the 0.5m reinforced concrete wall to vault
After seizing jewellery and other valuables from 72 safety deposit boxes, they escape in a waiting van
The contents of at least 56 safety deposit boxes were taken from the vault after holes were drilled through a 6ft (1.82m) thick wall in a raid which lasted four days.
Det Ch Insp Paul Johnson described the gang which carried out the heist as "highly audacious".
Scotland Yard originally claimed it was alerted to the burglary on Tuesday 7 April.
However, it later emerged the force had been told an intruder alarm was activated on Good Friday but decided it did not require a response. The force is now investigating.
Hatton Garden is famous for jewellery and the vault was used mainly by local jewellers and gold dealers.
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