Just because you've lived there, does not mean you are going to notice problems.
The town were I grew up had (several years prior to my arrival) a bunch of asian gangs that popped up after it imported a few loads of refugees. While you would be hard pressed to see a clear rise in the murder statistics, there are certain neighborhoods where the people who have lived their a few decades can tell you very consistent stories about where the prostitute houses where, who got killed, where the drugs were sold. Just because someone got murdered, doesn't mean they'll pad the numbers of a government database for an internet private eye to point his finger at. And the people in the neighborhoods where the gangs haven't set up shop may have no idea about what goes on a street over.
It ended after the police conducted two stings that managed to net most of the fuckwits, who were subsequently jailed and deported.
Mostly ended anyways. Before I left the town, another whorehouse/drugden was raided, which was incidentally next to my favorite restaurant. I had walked and stared at the place dozens of times. Never suspected a fucking thing.