Thought about that remark about opening car doors underwater .
Hm. Water pressure force on the door, assuming 9 feet in average depth and a 4 sq ft door is over 2,000 lb if my arithmetic is correct.
I'm not signing this one 'cause I'm not sure my 'rithmetic is correct.
Several iterations of ASTC (Aviation Survival Training Center) school lets me tell you that no, you're not getting the door open until the vehicle pretty much completely floods. The first time I went through it from the inside of the "aircraft", I was an experienced govt diver (so completely used to being underwater and with "out of air" emergencies), upside down in 10' of water in controlled conditions with a Navy trainer on SCUBA holding a spare regulator a few feet away in case I panicked. I was still pretty creeped out my very first time as the water covered my head and I knew I had to let it completely fill the cabin before I unharnessed myself and wormed my way out. Even creepier the first time they made us do it with blackout flight helmets. Even though you think you would know, via gravity, which way is up, you don't.
The whole process of the dunker dropping into the water, turning upside down (by design) and filling with water, then coming to rest on the bottom, then me finding referencing points and finding my way out my designated door or window and getting to the surface was maybe 1.5 minutes, with me holding my breath about half that long*. I knew what was coming, knew I had rescue if I tapped out, and practiced a lot before my first class. Now think about the thieves in this situation with no training and no discipline. It would be hazardous for someone on SCUBA, in clear water, daylight, and no mud or other extraneous dangers to deal with them. That is if they didn't go full panic and breath in water immediately after the vehicle was flooded to open the doors.
*Try and hold your breath. Many people, in a totally relaxed state, can barely hold their breath for 30 seconds. You can certainly train yourself to hold it longer, but now add panic and exertion, then cut whatever your relaxed breath-hold state is in half. I'm betting the thieves breathed in water within 15 seconds of the car filling.
Here's an ASTC video to give you an idea of being trapped underwater (about halfway through the video):
https://www.youtube.com/watch?v=WRuNDA7qJBU