Hatton Garden heist
Thieves drilled a hole through a half-metre thick wall to enter the Hatton Garden vault Metropolitan Police

Partners of people who use specialist drills like the one used in the £60m ($100m) Hatton Garden heist are the subject of an unusual appeal by police investigating the dramatic crime.

They have been asked whether they have noted any "odd" behaviour in their partner, since the theft, earlier in April.

"We are keen to hear from wives or partners of anyone who has specialist knowledge or skills that use this sort of equipment," said Detective Sergeant Craig Turner.

"Were they away during the Easter bank holiday weekend or have they been acting oddly since the burglary was carried out?" Turner said.

The theft gang used a diamond-tipped Hilti DD350 drill to bore a hole in the half-metre thick wall to get into an underground vault housing boxes of valuables worth millions of pounds at Hatton Garden Safe Deposit Ltd.

There was criticism from safe box owners after it emerged no officers responded to an alarm that sounded while thieves were midway through the raid.

Police investigating have so far drawn a blank in the search for suspects, despite a £20,000 reward for information being offered. They continue to scrutinize thousands of hours of CCTV video for clues.

"The hours of forensic work and inquiries have been vital in order to ensure we are able to exploit all investigative opportunities to their fullest extent and assist us in identifying those individuals responsible," said Turner.

The drill used by Hatton Garden gang
The drill used by the Hatton Garden gang Met Police