Most information is gathered through Public Databases and Public Records. However there are some things that are not accessible by the General Public Websites. Items not available on Public Websites or Public Databases will require that the seeker obtain a Warrant or Subpoena. Law Enforcement, Justice System Personnel and Private Investigators are the only people who are privileged to that type of information.
All Law Enforcement use a system called NCIC, which is only available to Law Enforcement. They have to use a special code that is assigned to them their entire career. Misuse of this type of database cares a 250,000 fine with time in jail. Both for the Officer and his/her agency is cited with the fine. Information access comes with some risk and penalty when it is misused.