I would also suggest surveillence cameras. Hidden ones. So if one of your chickens just happens to "wander" into thier yard again, thru a six foot padlocked coop, you'll have proof. Sounds to me like they stole them. I would also report it. That way, if they get any ideas again about eating a wandering rooster that they know is yours but it walked into thier back yard by its poor little self<yeah, right> you'll have a record.
Rammy