With mounting speculation since the robbery occurred that it was an inside job, the source makes another startling claim: the robbers were able to let themselves in.
The first three suspects arrived on bicycles clad in black jackets at 2:18am.
"They clearly knew the security code of the main doors, and let themselves in without any problem at all."
The remaining two men arrived on foot fourteen minutes later and used the same entrance to gain access to the building.
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DNA traces have been found inside the apartment Kardashian was staying in, a source told AFP last week.
It comes as French prosecutors formally opened an investigation into the robbery in which the US reality TV star lost millions in jewellery.
The investigation is focusing on "armed theft in a gang, criminal conspiracy and kidnapping," another source said.
The men who burst into the residence in the early hours of October 3 tied up Kardashian and stole jewellery worth around $14 million.
