Yes, it is a good question. And it's something that I've had go through my head several times in attempts to answer it. Thankfully it hasn't been an issue yet so I haven't had to come up with the answer, but...

Any demon is not innocent in Angel-sense. Even if the demon hasn't done anything bad, yet. Haha, poor demons.

Uh, as for humans/wanderers/and the like... the definition gets a bit hazy and more difficult to define. Murder is definite in the not innocent. Cold blooded murder. Rape. If someone is guilty of those traits, they are not considered innocent and can be killed by an angel without a loss of wings.