Certainly we wouldn't normally expect the police during the course of an investigation at a crime site to change the crime site by replacing something that what was present at the crime site would we?
Somebody was upset with the flag on the house, and instead of just removing it, they replaced it. Who and why would be very interesting to know.
Probably just some Puerto Rican neighbor who was ashamed to see the PR flag there. That person probably wasn’t the one who had put up the American flag and therefore just simply left it there.
But why somebody would have put up an American flag at such a place, I don’t know.