You’re backtracking a bit, but not enough. You originally said, “Of COURSE he is a rodeif. He already killed several people.“
This is simply not true. Having committed murder in the past does not give one the status of a rodef, and no one is allowed to kill a murderer.
The reason a baby may be considered a rodef is because it is currently, definitely endangering the mother’s life. Assuming that someone wants to kill you just because they’ve killed in the past is also incorrect.