What do cops wear underneath their uniforms?

Before I launch into this, please know I am not being pervy. I am writing a book (my first) and would like everything to be as realistic as possible. It's a murder mystery/thriller with a slight supernatural bend to it. In it, a police man who is one of the main characters gets abducted and is forced to disrobe. My question is, does anyone know what they have on underneath their uniforms? I have heard just regular underwear, to jocks, etc. Again, I am doing research and would like an honest answer. Thank you in advance!