Maybe the account that was accessed online was an account that was in the son's name, but managed by DW. For example, when you're a kid and your grandparents open a savings account for you and they put in the money, make deposits and hold the account book, etc.
Anyhow, if the account is in David N. Westerfield's name, maybe the username could logically be DNWest1 - if the account is managed by DW, it would make sense that he would pick a password/PIN that he could remember.
I don't know, it just kind of dawned on me all of a sudden when I read Val's post.