Here's another one for the Mystery Writers of the World.

Sometimes, you can't figure out who the killer is by seeing which story doesn't add up with the rest. The stories might not add up because people forget things. Or they remember wrong - they think they saw a tall redhead, they really saw a short brunette. And the colder the case is, the more likely it is that they will have these little gaps and errors in their memory.

Really.

It's possible they're lying, but it's probable that they're just mistaken.

And not just one of your suspects - every last one of them is going to say something or other that doesn't mesh with what you think you know. That's why people like hard evidence such as videos. When we say the camera doesn't lie, we also mean it doesn't forget easy.