Heck,i've been wrapping my head around a detective game concept since two years ago and i found this topic only now!
I've got TONS of ideas for such game,the catch is explaining them via text,heh!
One possible feature could be a "Deductive Reasoning Phase" where,when the player thinks he has enough hints and proofs,to "connect" thoughts using said proofs/hints as a link.
much more like this
Of course taking a path wouldn't exclude the other ones,but it will take time to find out.And you may lose track of the suspects like this!
The passage from a "Thought" to the next one might be "blocked" by a question such as:
................................................................/Who?--hint
A)OMICIDE---[Proof]---If it is Omicide then--| How?--evidence
................................................................\Why?--questioning
or: B)SUICIDE---etc. etc.( don't want to write the map again! :|)
I'd suggest to not use any official characters;It's a real pain in the back.
I'd LOVE to help out for the graphics and the characters/plot,if you guys want!
Oh yeah there are more concepts to add to this,which is just a tiny part of a whole gameplay!
I just have to recollect my Game Designs Sheets Notebook.