Can a citizen file criminal charges against the police if the department refuses to?
This part of the question is dependent on the location, some area will let citizens file complaints against police officers directly to the courts; others require it to be filed with the districts, or state's attorney's office.
It should be note that there is Prosecutorial discretion in determining which cases are taken up.
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.
If you feel the police department where the complain is filed isn't being taken seriously then there's always the option of moving up the chain. A complaint can be made with the sheriff's office, state police, or with the state's attorney office.
Can you sue a police officer?
Bob can sue the police officer individually under Section 1983 of the Civil Rights Act of 1871
Should proactive legal action be taken?
For this hypothetical, the answer is that it shouldn't be the first step. These are tickets, if you disagree with a ticket you always have the option to fight it in court. If tickets continue to roll in even after the original tickets were resolved then more action would be necessary