A Hatton Garden-esque gang may have brought their own toilet to use to avoid leaving any clues behind.
The robbers – who drilled into a bank vault over Christmas – broke into more than 3,000 safety deposit boxes.
But cops now thing the smart gang knew they couldn’t go to the toilet during their heist.
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If they had not had brought their own loo they would have left their DNA when doing so.
They were there for at least 46 hours.
Police were alerted by a fire alarm at 3:59am on 29 December.
Responding officers and firefighters discovered a huge hole leading directly into the basement vault, where the boxes were stored.
The Sparkasse branch had been closed since Christmas Eve, and police believe the suspects exploited this, gaining entry via a multi-storey car park.
Police in Gelsenkirchen, Germany, are still trying to identify the suspects.
They have released images of three masked individuals – though reports suggest at least four were involved – and two vehicles, appealing to the public for information.
Local media have revealed that the crooks sprayed an as-yet-unknown chemical all over the vault, apparently to destroy DNA traces.
Toxic fumes mean cleaning is ongoing, and staff must catalogue the items left behind before the branch can reopen later this week.
Around 95% of the approximately 3,250 safe deposit boxes were broken into, leaving only about 150 untouched.
More than 1,000 customers were affected, and police reports will be filed on their behalf.
Experts believe the burglars had prior experience with core drilling, as reported by NeedToKnow.
Drilling overlapping holes through the 40-45 cm-thick reinforced concrete wall would have taken two to four hours, likely using a 20kg (44lb) diamond-tipped core drill.
They may also have brought jerry cans, a pump and hose to cool the drill, and possibly provisions and the portable chemical toilet.
The suspects remained undetected in the vault for at least 46 hours after breaking in on the morning of 27 December, escaping with cash, gold, jewellery, and heirlooms worth more than €100m (£86.6m).
Police believe the burglars likely had an insider accomplice who provided crucial confidential information – possibly a current or former employee, or a contracted worker.
There are no CCTV cameras in the building’s basement.
The investigation continues.
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