I really appreciate your help!
I don't know his previous owner besides the horse trader. While her husband was in the hospital with heart problems she was pocketing his moeny to pay bills. The family found out. She was the Grandpa's thrid marriage, I believe. She fled and no one knows where. She left all of their animals behind: horses and dogs mainly.
I have no way of contacting her. And she told me the last time I saw her that she didn't remember much about Blu.