Police often have direct influence on whether or not an act comes to be
regarded as a crime.
May let someone off with warning if they come from a "good family", yet
arrest someone who does exactly the same thing because he/she is a
proactive policing-actively searching for specific crimes(patrols, etc)
reactive policing-respond to calls; at request of the public Reporting Crimes
Many crimes do not even come to the attention of the police.