One could consider terrorism to be the ultimate crime, yet an argument can be made that terrorism is the best thing that could happen to reduce crime. Why? Eric Gould and Guy Stecklov argue that terrorism increases police presence and keeps people at home. They use data from Israel and analyze various types of crime and show that property crimes and assaults, even domestic assaults, are down after a terrorist event. But would this be the same in Europe or even the United States.
The type of terrorism Israel faces is a different threat than the one Western countries face. It is what I would call "petty terrorism", the bomb carried by a single person to areas otherwise of no particular interest. It appears Western Europe and especially the United States faces a more organized terrorism towards high-profile targets. A threat in the latter case would thus draw police away from the neighborhoods to the airports and landmarks, thus leading to higher crime.
Imagine if all those airport security personnel were cruising the bad neighborhoods in the US. Far fewer people would die violently.