I get that God gave us free will, but hear me out. If a police officer was to catch a man getting ready to shoot someone, they would obviously intervene, and this wouldn’t be taking away free will.
Why doesn’t God do the same thing? Intervene to stop atrocities like murder?
Have you noticed you use a police officer as an example? Why? Let’s replace that police officer with a random private citizen. Will the example work? No, it doesn’t work. The private citizen is not certain to intervene directly and we do not demand that he would. In many cases it is enough for him to ask someone else to intervene (that is, to call the police).
So, what’s the difference? Police officer has promised (or sworn) to fight crime and is paid to do so. Private citizen has made no such promise.
So, has God made a similar promise to intervene directly to stop every murder? Doesn’t look like that. Thus it doesn’t look like He has a duty to do so.
As for that asking someone else to intervene, God has given each of us a conscience. Shouldn’t that be as good, as calling the police?
Now, sure, we make lousy “policemen”. But He’s working on it…
For that matter, aren’t many of those cases we’re dealing with evil similar to training exercises? And in that case your question becomes “Why didn’t instructor just do the job himself, instead of waiting for trainee to do it?”. I guess the answer to this question is obvious…