Might be a language thing - you have 0 crimes committed, but you do have 6 criminals in the city. You're right, detectives do their "stake outs" and they're the only ones that can take out criminals before they commit a crime. I feel like you, I don't like having criminals in my city at all, but realistically - there's probably very few cities out there that in real life that no criminals at all.
It took me a long time to realize that the goal *seems* to be 0 crimes, not 0 criminals. Since you're catching some of them before they commit a crime, and you have enough good police coverage to apprehend them when they try to commit a crime, I commend you for your well-run city! Your thoughts on abandoned buildings being due to criminals is an interesting one; I haven't personally seen this in my game, but haven't watched it as closely as you have, so it might be the case.
In any case, if there is a bug, unfortunately the game is no longer actively developed nor supported, except for users like us. There won't be any more adjustments to SimCity 5, so we can only learn to manage our cities as best we can with how the game works now. Happy Building!