This is a very probable scenario and has most likely happened before.
I would not be opposed to a safe psychological interrogation technique like waterboarding. It does no damage if done properly.
Even if the detainee is innocent it comes down to this - A potentially innocent person thinking he's drowning for a few minutes or multiple 100% innocent people being killed if we don't get the information.
If proper waterboarding has saved at least 1 innocent life, it's worth it. Any innocent people waterboarded might have been scared, but they are still alive and uninjured.