How can the law be changed to allow civiluans to charge the cops with a criminal not just civil offense?

simple get the legislature of that state rewrite the law. Now, first you want to see your state rep. and get a petition once you have enough support is when the fun begins. You get to fight special interest groups (Police) that lobby the legislature to ensue such a measure is not voted on or debated. These groups have deep pockets, make u look homeless. it can be done, but the groups would bury you, but go for it.

There are already checks and balances in place that provide for criminal prosecution of police when there is evidence that they have acted outside the scope of their authority. There may be some instances when this system doesn't work, but those are few and far between. If there was more respect for the police in enforcing the law and less sympathy with the criminals committing the crimes we would all be better off.

adoption of a mandatory prosecutorial system would do the trick. in most non-U.S. countries, prosecutors are obligated to pursue well-grounded criminal complaints brought by citizens. in contrast, in the U.S. prosecutors have full discretion whether to charge someone with a crime. they are free to ignore legitimate complaints of criminal activity, and frequently do. because most prosecutors are elected officials, their prosecutorial decisions are often politically-driven. in practice, this means prosecutors are reluctant to charge the police with crimes unless the evidence is unusually strong, because it will lead to prosecutorial-police tensions, and may lead to political backlash,