Each State has its own "theft" laws. Whether it is "theft" or "appropriation of lost property" is defined by how the law is written. Although, it may (or may not be) "theft", it may be "appropriation of lost property." Speak with the local law enforcement. Ask for a copy of the report, it's public record and should be available to the victim of a crime. Ask to speak with the "watch commander" or "sergeant" or whomever leads the division. Ask them what they can or will do. Entreat them to file with the D.A. In the meantime, protect your flock, photograph each bird for identification purposes, and build a run for them. Continue to build a positive rapport with your other neighbors.
It may help for you to know why your hateful neighbor did this. Knowing the "why" will help you to protect your chickens. It doesn't mean you have to accept the reason, but knowledge is power, especially for protecting your house and loved ones.
I hope this turns out well for you.
