I'm having difficulty finding the article, but there was a news story that the single most data request from the London Crime cameras being.. flat managers requesting footage of people who didn't clean up after their dogs.

Cameras don't prevent crime. They may shift crime (if you have cameras and your neighbor doesn't, guess whose house is going to get burgled first?) and they may make crime easier to prosecute after, but they do not stop crime in any meaningful way.

And more than likely, the people who are spending a lot of money to buy and monitor those cameras don't really care about the shoplifters and graffiti artists - those crimes don't cost very much of society and stopping them is a low priority. Serious crimes like murders and home invasions are.. actually pretty rare and cameras generally don't catch them.

If you're spending millions to install cameras, record them constantly, and store all that footage in a way that's searchable.. it has nothing to do with crime. It has everything to do with monitoring your population.

Edit:

Found it: http://news.bbc.co.uk/2/hi/uk_news/magazine/7469369.stm

I did some research, because I had trouble believing that the cameras don't deter crime. They do deter some kinds of crime (e.g. theft in the areas with the cameras) but not violent crime.

I'm really quite surprised, you'd imagine having a bigger chance of getting caught would make people stop and think.

Probably the reason is, as you say, that those types of crime take place where the cameras mostly aren't, like indoors.