The Police Quest series by Sierra.The less popular series back in the late 80's, compared to King's Quest, Space Quest and of course the teenage boy's favourite of Leisure Suit Larry. All were good series (Sierra were killing it from the mid-80's to mid-90's until they changed owners), but this one never got the attention it deserved.
oh how i loved that game, took us so long to finish it, a group effort in the end with the help of someone's mum. The place we got stuck was finding the right words to ask the hooker who was in jail to give us evidence, had to be asked correctly or you couldn't advance.
I played this more than any of the other Sierra games - though I did give Manhunter a go, which was a bit of a weird one, never got anywhere with it.