In Batman: Arkham City there are "green" criminals that you can interrogate for the Riddler's stuff.
Are these same green criminals available for interrogating in Batman: Arkham Asylum?
In Arkham Asylum there are "Secrets maps" instead of the Riddler informants that are in Arkham city. The maps serve the same purpose, but are slightly more difficult to find as they don`t stick out as much as the green henchmen do.
Here is an example of one of the secrets maps: