The intelligence of individual officers is not the issue even though smart candidates are actively discriminated against in some locations (see: http://abcnews.go.com/US/court-oks-barring-high-iqs-cops/sto...). Prosecutors control the entire process and have largely negated trial by jury through the use of multiple charges and plea bargains (see: http://criminal.findlaw.com/criminal-procedure/plea-bargain-...). Many prosecutors are not directly elected, so the ballot box does not provide a direct path to a solution. Furthermore, I doubt many voters vote for candidates based on who they will appoint as a prosecutor.