I say get a shot gun and wait outside your pens at night, lol. I doubt the person who took them would come around any more if you had a big dog or a man with a shot gun waiting, lol.
OMG who would do such a cruel and horrible thing? Do you have a local newspaper? Contact them and see if they'll do a story, might be enough to scare whomever did it and have others on the lookout.
Wow, your law enforcement doesn't sound too promising.
I would think you have a better shot at going the "no tresspassing" route. Tell them someone has been has been tresspassing on your property and you are more likely to get some assistance.
Do you have signs posted? I would get some up asap, they work in your favor should you actually catch this person.
Also, did you tell the police the VALUE of your birds? Muscovey aren't cheap, especially the more rare colors.