Whoa!! A lot happened while I was sleeping... And none of it good :(
So sorry you didn't manage to get the colt.
This is what I think you should do (I am not a lawyer, or a cop, and I do watch law and order occasionally, but as a citizen with rights, this is my opinion).
Print out and collect all evidence (photos, receipts of tetanus shot etc) that you have of your mare being pregnant, and the foal after it was born. Go to the police and file criminal charges of theft, write up a very long and very detailed affadavit... Write down everything everyone said/times etc, especially write down what the BO said to the cops in both instances, because he went back on those statement.
Then, call a lawyer... There were some links on here, have them do something right away... Perhaps they can stop the BO from moving or selling the colt before ownership is proven.
Actually, call a lawyer first. I think the law is on your side, so this guy cannot go on bluffing forever. But do it first thing in the morning... So the process can start working.
For your sake I hope the BO pays over and above what is even necessary for what he has done to you. Who does he think he is?? Above the law? He cannot just make up things as he goes along.
Take him to court and make him pay for being such a (what word can I use?)
Posted via Mobile Device