I lived in Los Angeles the year of the L.A. Riots. The LA Times reported that the added police mobilization the week before the Rodney King verdict in Los Angeles this April reduced violent crime by 12%. However, the cost for that week of relative calm was over $8 million for the additional security only, not the regular weekly police costs. The week after the verdict, major crimes sprang right back up again. Clearly, occupying every corner with police and National Guard is not a good way or a humane way to reduce crime.
It is interesting that on the basis of these paltry reductions in crime Chief Williams used the new crime statistics to urge passage of Proposition 1 on the city ballot which would provide the money to the LAPD for 1,000 new officers.
Now compare that with the project in Washington D.C. where a 14 to 23 percent reduction in violent crime was achieved for less than one twelfth of the money spent per week. Suicide calls in the District were 30% less and rape hotline calls were 50% less. Also, rather than springing right back up, the crime rate took months to return to it's previous rate.