At no point does it become yours. I'm pretty sure that, while you can't necessarily prosecute the person currently in possession, you could almost certainly recover the property if you could prove it was stolen from your estate.
Added: In most English speaking countries it becomes a crime to willfully possess stolen property as soon as you know that it is stolen. In general, the lack of mens rea in merely possessing stolen goods would make it enough to repatriate the goods, but if that's not enough, most statutes on the matter explicitly state that you must know and wish to unlawfully handle the stolen property.