Here's an idea.
When a citizen gets robbed, have the citizen store a report:
public class report{
Thief offender;
Time timeOfOccurrence;
Citizen victim;
Vector3 location;
Item[] stolenItems;
}
After the citizen gets robbed, have the citizen run around looking for a guard. It could be random running until the citizen finds a guard via Physics.OverlapSphere (to simulate the effect of not knowing where the guard is) or they could run to the nearest Guard Post where guards are usually standing.
When the citizen finds a guard, it tags them and the guard and citizen move toward each other. Once within range, the citizen gives it's report to the guard. The guard then paths to report.location and looks around until it finds report.offender.
If the guard doesn't find report.offender within x amount of time after report.timeOfOccurrence, the guard gives up and goes back to his post. The report remains, but the guard no longer actively searches for report.offender.
When the guard finds report.offender, they chase him down and get back report.stolenItems, incarcerate report.offender based on the value of report.stolenItems, and go back to report.victim and give them back report.stolenItems. The report is then disposed of.
This of course is a very old-fashioned representation of law enforcement. In a more modern setting, citizens could call in a report to a dispatch center who would then relay the report to nearby lguards.
In summary, I like to create classes that store information and exchange those class instances between scripts. Think of how packets of data are sent through the internet. The machines that send them might be different, but they can understand the data inside the packets, so communication is possible.