The number of police officers per capita increased by 30% from 1960-1970, but increased only moderately after that, peaking at about 40% above 1960 levels: https://eml.berkeley.edu/~jmccrary/chalfin_mccrary2014b.pdf. Violent crime rate more than doubled from 1970 to 1990 while police per capita went up only 10-20%.

Moreover, the overall increase in violent crime tracked the homicide rate. Homicides are very well reported, throughout the modern era. The homicide rate doubled from 1963 to 1973. That almost certainly reflects an actual increase in homicides, or just previously unreported homicides being reported due to increased policing.