If you have reasons to be suspicious, those ones that the police should consider, it is a good idea to report them. The people that tries to circumvent laws for their benefit, mostly lucrative, do not deserve to be tolerant with them. Doing so, you also could help others because anyone might be damaged, in any situation.
Reporting is very simple, you only need to search for a policeman and speak about your concerns. In a police station there are multiple ones, so you decide. Any policeman in almost any part of the developed areas, has the duty of analyzing those concerns and, if they are relevant, to start actions toward the subject.
A bit of collaboration with the security forces helps in the task of avoiding problems caused by who doesn't respect the laws and their goals, that protect citizens.