The letter says the B"D "affirms an abuser us considered a rodef at the time of the attack."The only logical reason that they went to pains to add "at the time of the attack", is to indicate that is the only time he is considered a rodef. Once the attack is over he is not a rodef.
The conclusion should be that you can kill the abuser at the time of the attack but afterwards you are to call the police.
He is a Rodef as long as he is considered a (potential) public menace. There is no Din of Mesira with a perpetrator of this variety who has not been brought to justice.
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