Karl Keating’s book Fundamentalism and Catholicism dedicates a whole chapter to Bart Brewer and his organization Mission to Catholics. In an edition of This Rock, Karl notifiies his readers that Brewer had passed on and needed our prayers.
Brewer was, according to him, raised Catholic, became a priest, but after reading the Bible found that Catholic beliefs and the Bible didn’t match up. He went through several Protestant denominations including SDA and I belief (it’s been a while since I’ve read the book) ended up a Baptist. He went around giving talks about how the Catholic Church was wrong.
Hopefully this helps a bit.