Have you ever had the courage to make a citizens arrest of the guy for murder?
Now that is a really good question.
Thought about why that hasn't happened: But the reality is that no ordinary citizen would be allowed to get anywhere near such a protected space, and to effect such a thing you basically have to be confronted with the crime - going looking for it would end up being reasonably characterized as "vigilantism".
But I believe it has been tried in the past - Operation Rescue in the 1980s. Didn't get them anywhere.