Are there hints for all of Riddler's trophies?

In Arkham City, you can interrogate enemies to get hints (markers on the map) of where to find Riddler's trophies. I've finished the game now, and finished all sidequests, but I still have 6 trophies to find (spread between Park Row and Amusement Mile). Problem is: I've soaring Arkham for a couple of days now and haven't found anyone to interrogate anymore.

Therefore I ask, is it normal that there are no hints for the last few trophies? (Am I meant to find them on my own?)
Or should I keep looking for people to interrogate?

Never mind, I was mistaken. Turns out all these trophies (which I thought were missing) were inside buildings (like the courthouse or the church). That's why I wasn't finding their markers on the map, they weren't on the main map.

I feel a little silly that I spent two days looking for an informant. =/