Evidence from research into the effectiveness of CCTV for reducing crime indicates:

• CCTV has a small effect in reducing property crime in some circumstances. Crime reduction effect of CCTV primarily depends on other factors.
• CCTV has zero effect on reducing violent crime.
• CCTV can reduce property crime in car parks providing other effective CPTED strategies are in place. Maximum crime reduction is ~16%.
• CCTV crime reduction effects are time limited (crime reduction drops off over time).
• CCTV causes crime displacement in line with limited effectiveness in crime reduction.
• Crime displacement from CCTV was identified as research areas increased. Crime disaplacement can be in crime type, time or distance.
• CCTV is an effective support for Police in satisfying their KPIs for closing cases.

Research papers are available here.