Scott Disick's home was almost certainly broken into by someone who knew him and knew the property ... law enforcement sources tell TMZ -- not that Scott seems the least bit concerned.
Our sources say it appears Sunday's burglary was an inside job, because the crook or crooks knew exactly where the security cameras were before breaking into the house through a backdoor because they moved the cameras so they could enter undetected. After entering, they opened a bunch of drawers.
Cops also believe the burglars knew full well Scott was out of town, appearing at a gig in Vegas for his birthday. It was heavily advertised beforehand.
Scott was back home by Sunday around 9 AM, hanging with friends and rambling incoherently. Seemed like the party was still going from Vegas, and he was NOT sweating the burglary.
The break-in comes almost a year to the day from the time Scott was hit the first time ... someone broke into his home and stole some super expensive watches. Law enforcement tells us Scott believes he knew who did it but didn't want to rat them out.
As for what was taken this time around ... we're told an inventory hasn't been taken yet.