Any stats on the effectiveness of video surveillance are hard to find. The Met police in London are claiming that CCTV now accounts for six crimes solved per day:
BBC News - "Six crimes a day" solved by CCTV, Met says
... The number of cameras in Britain has gone up from 21,000 in 1999 to 59,753 in 2010, it added.
The Met said among the 2,512 suspects caught this year, four were suspected murderers, 23 rapists and sex attackers and five wanted gunmen.
I'm curious what that translates as in cost per arrest?