Preventative not corrective. The following are far cheaper than building more prisons or increasing punishment after crimes occur.

1. Fix physical environments (cheapest, fastest wins). Improving lighting alone reduces crime by 20% on average. Cleaning and greening vacant lots also reduces crime by a measurable degree.
2. Put police where crime actually happens (cost effective). Crime is extremely concentrated—often 50% of crime happens in less than 5% of places. “Hot spot policing” consistently reduces crime in those areas.
3. Help offenders reintegrate (moderate cost, long-term payoff). Job placement, housing, substance abuse treatment, and mentoring significantly reduces recidivism, which leads to fewer future victims and repeat offenders.
4. Invest in kids early (highest ROI, slow payoff). Although it takes decades to see results, early childhood programs, family support, and education prevents future criminals.