It is very difficult to attribute the effects on surveillance on crime simply because there has not been an establishment of an exclusive causality relationship between surveillance and crime.
The presence or absence of surveillance is but one of many factors that may or may not have an effect on criminal activity.
On the other hand, it is very easy for politicians to create a relationship that they can use for their own political purposes.
What is especially risky is to make an inference concerning surveillance and criminal activity based on a correlation between the two.... but people do it all the time.
Correlation does not mean causality or if you want to be a pomopus jerk like me:
cum hoc ergo propter hoc 