They added them in a software update at some point in 2019. It gets recorded to a usb drive that you keep attached. Any drive works, I personally prefer an external ssd.

When you press the record button, it dumps the past 10 mins of video from 4 external cameras onto the drive. When the car is fully stopped, you can either watch the video on the screen inside the car or unplug the drive and watch it on your laptop or on any other device that can read from usb/external drives.

There is also an automatic (aka sentry) mode that triggers dumping a video by any nearby action, but that's only when the car is parked and left unattended.

I don't know if it was even a Tesla car, but if it was they're sorta famous for having cameras out the yin-yang, I've seen lots of 'vandals caught by Tesla security cameras' puff pieces.