Kendall Jenner, Jewelry Theft an Inside Job

Kendall Jenner was not burglarized, despite what she told cops ... it was definitely an inside job, according to law enforcement sources.

TMZ broke the story, Kendall reported the alleged burglary at 1:15 AM Thursday after she realized $200,000 in jewelry went missing.

Our law enforcement sources tell us what really went down. They say Kendall was having a party with a bunch of friends Wednesday night. At some point in the evening she heard an alarm warning that someone opened a door, but she thought nothing of it.

We're told Kendall left at midnight, leaving her friends in the house. When she came back just after 1 AM she discovered her jewelry box was open, and that's when she called the cops.

Our sources say there was absolutely no sign of forced entry and they are certain the thief knew exactly where Kendall kept her bling.

BTW ... if the person who steals stuff inside a home was invited in, it's not a burglary -- it's the crime of theft.