What two things do PSD divers do?
quick guess -- search and rescue? (and unfortunately not enough of the second part... probably more recovery than rescue)
Recover Bodies and search for evidence.
If one of them isn't ask questions you need to extent that to "what three things..."
Seriously,
Is it like cops, Protect and Serve
PSD do one of two things, They ether find what they are looking for, or prove that its not there. there for they have to use a very simple search pattern and be able to document where they have been so that the next diver can take over and complete the search. think about this the next time you find some thing and have to go back and get it.