Perusing some 19th-century grammar books for another purpose, I came across an interesting etymology:
"According to Grimm 'shall' or 'skal' is the preterite or perfect of a verb meaning 'to kill'. As killing involved the payment of the penalty of wer-geld, 'I have killed,' came to mean 'I owe the fine,' and thence 'I owe' simply."
-Mason, C.P.. English grammar, including grammatical analysis. London, 1890.
I became curious, but was unable to find any corroboration of this etymology younger than the 1800s. For the details of the claim, I managed to find Jacob Grimm's original assertion(in German):
"Skal debeo setzt skila voraus, aber der begrif, welchen ich diesen wörtern beilege, wird überraschen. skila muſs heiſsen ich tödte oder verwunde, skal ich habe getödtet, verwundet und bin zu wergeld verpflichtet. von skila ist übrig das goth. skilja lanio schlächter, tödter."
-Grimm, Jacob. Geschichte der deutschen Sprache. Leipzig, 1848. pp. 902-903.
Is anyone here expert enough in Germanic studies to prove or disprove this etymology?