Your comments on the number of police involved responding to a simple call isn't too far off, but it isn't that simple.  First, you still require a minimum number of patrol members on the road, to ensure there is coverage for more serious calls.  The real problem lies in the legal system that has made it so difficult to investigate any major case, and charging someone with murder, or manslaughter for selling bad drugs is just that.  

If all the police had to do was arrest the person, charge them and walk away, it would be easy.  But case law now demands huge amounts of disclosure evidence from the police relating to every charge.  And, guess how that is done, by hand, compiling and vetting each document.   There is no computer program to do it totally.  You would be amazed to find the number of people employed in every police office dealing with just disclosure issues.  If the disclosure isn't complete, the bad guy walks.  It is more complicated that that, but that is the start.