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I've sort of given you the basic result before anyone even said "I interrogate the prisoners," just to save time.
But, if you want to try to get more out of the prisoners, you'll have to be specific, through narrating your actions and/or rolling. Note: much can be accomplished through narrative, even if you don't have anything specific on your sheet to roll. (You can always pick an attribute that seems relevant and try to roll under it.) I'm not saying there's more to be had or that this group has the means to get it, but that's how pursuing that goal would work.
By the way, this is a good example of how generic actions get generic results. There's nothing wrong with that. It saves a lot of time and moves the game along, but it gets you kind of the average result. Like the difference between, "I enter the room" and "I carefully listen for sounds and spy around the corner..."