When a police officer pulls you over, there must be probable cause to stop you. Police officers are not allowed to simply pull you over and start investigating without a good reason. In some cases, even when police claim to have probable cause, careful analysis of the traffic stop reveals that they really didn't.
Police departments throughout the United States are increasing their use of body cameras on police uniforms. The idea is not only to collect video evidence against defendants, but also to protect against police misconduct and violation of people's rights.