I can provide some general advice on how one might approach a situation like this.
If you witness someone stealing from your neighbor's mailbox, it's important to consider the best course of action based on your judgment and local laws. Here are some options:
Assess the situation from a safe distance: First, make sure you are safe and not putting yourself in harm's way. If you can observe the situation discreetly from a distance without risking your safety, it may help you gather more information.
Call the authorities: If you believe a crime is being committed, it's generally best to report it to the police. Call the non-emergency number of your local law enforcement to report the incident. Provide them with as much information as you can about the suspect and the incident.
Notify your neighbor: If you have a good relationship with your neighbor and feel comfortable doing so, you might want to inform them of what you witnessed. They have the right to know if their property is at risk.
Document the incident: If you can safely take pictures or video of the incident and the suspect without endangering yourself, it might be helpful for the police investigation.
Avoid confrontation: Confronting the person directly could be risky, as you don't know how they might react. It's best to leave law enforcement to handle the situation.
Know your local laws: Different areas might have different laws about citizen interventions in such situations. Familiarize yourself with the laws in your area to understand what you can legally do.
Remember, the safety and well-being of yourself and others should be a priority. Reporting the incident to the appropriate authorities is often the best way to handle situations involving potential criminal activity.