Well, some good day I was searching something on Internet and then I don't remember why but I finished reading the FAQ's of the website of the
Church of Satan 
I don't remember if it was one or two months after that but I remember that I was walking in the street when I saw a kind of bookstore that sold old books

I looked through the books and I found a copy of the satanic bible (in Spanish) I bought it and I read it in detail.
Since then I consider myself as satanist

It happened when I was 13
