Khloe and Kourtney Kardashian -- Film Crew Supected in Thefts

The Kardashians have a Benedict Arnold on their TV show ... a thief ... a jewelry thief ... at least that's what law enforcement sources believe.

TMZ broke the stories ... $250,000 worth of jewelry was stolen from Khloe Kardashian and Lamar Odom's former Tarzana home, and $50,000 cash was pilfered from Kourtney's Calabasas mansion.

Law enforcement sources tell TMZ ... whoever stole Khloe and Lamar's jewelry knew exactly what they were looking for. The thief or thieves took only the very expensive items, leaving the rest behind. They knew exactly where to look and what to take.

What makes it look like even more of an inside job ... there was NO sign of forced entry at either home.

Our law enforcement sources believe someone from the crew of "Keeping Up with the Kardashians" is the culprit.

We're told crew members are being questioned, but so far no one has copped to the crimes.