FCPD has a nice site For you to report Criminal Activity like
Bicycle Theft
Civil Dispute
Destruction of Private Property/Vandalism
Larceny/Theft from Motor Vehicle or Parts
Larceny/Theft Under $5,000
Lost Property
Suspicious Person/Vehicle
Solicitor Violations
Telephone Harassment/Threats
Trespassing
Unoccupied Hit and Run Accidents
https://www.fairfaxcounty.gov/police/howdoi/communityreportingsystem