My first thought was Phone Booth, but someone beat me to it.

One that doesn't quite fit, but I also thought of Zodiac. Since it was based on an unsolved case, even though they interview a suspect, you don't know you if you actually see him or not. He is shown, masked or in the dark, in the cases where someone survived, but they filmed it with different body doubles so they never quite match from recollection to recollection.