PLEASE HELP! I think that the police violated my son's civil rights and I need a lawyer to fight this!?

Unbelievable. Your son drove drunk and KILLED four people, and what you're worried about is that they let him pee in his pants?? What kind of person ARE you?? No. The police don't have to allow him to go. When you commit a FELONY, you give up some rights. Bathroom breaks are one of those.