As someone who writes nothing but the pure, utter TRUTH, I have to say this:
In this situation, the police are not to blame. There is no law saying that they have to put their lives at risk in what would be a futile rescue operation (15ft underwater? Unless you've got diving equipment there is no way you're saving them).
I suspect people have been watching too much James Bond. You think you can just swim down to the car, punch a window and it will be alright. The reality is that it's freezing cold water, in your heavy clothing, and unlike James Bond it's not in the crystal clear waters of the caribbean, it's a muddy hole.