Why risk there being a lot of witnesses to a war crime? On the ground, there'd be much fewer.
Why interrogate someone in a helicopter if you can help it? Hueys are noisy machines, and I wouldn't want to try to understand a scared-to-death prisoner who speaks a difficult foreign language.
It's also pretty windy in a Huey. If the prisoner had maps (an interrogator's wet dream), the rotor-wash would be a nightmare.
You use whatever you need to support your position.