According to your bio, you live within the limits of the United States, so I'll assume this is the jurisdiction that is in question.
How to file a complaint Against the Police
Police departments take complaints on an officer in three different ways:
1: you can make a complaint online through the police departments website
2: A formal complaint can be filed by mail
3: A complaint can be filed in-person at the police department, during this process they will interview you about the issue and you are advised to bring a witness with you (lawyer, friend, or family member).
Once a complaint is filed in one of these three ways, the police departments internal affairs department opens an investigation into the matter to determine disciplinary measures. These complaints will stay on the officer's record permanently. Unfortunately, you will not be able to know the outcome of the internal investigation.
Can you sue a police officer?
Not only can Bob sue the police officer individually, but he can also sue the department the police officer works for under Section 1983 of the Civil Rights Act of 1871
How to sue the police for Misconduct?
In order to sue the police for discrimination or harassment, the victim must show that there is a pattern of this behavior; one incident of discriminatory or harassing conduct is not enough.
False arrest claims usually assert that the victim’s Fourth Amendment right against unreasonable seizure was violated. To prove such a violation, the victim must show that the police did not have probable cause, or sufficient evidence to warrant an arrest. If the police had probable cause, or believed that they had probable cause, then most courts will not find a Fourth Amendment violation.
A claim for excessive force maintains that the police used unreasonable force under the circumstances in dealing with the victim and typically, the victim suffers serious injury or death. There is no concrete definition of excessive force, so it is up to the victim to show that his or her particular situation did not call for the amount of force used by police.