Or HaChaim on Genesis 26:11/אור החיים על בראשית כ״ו:י״א

1 מות יומת, will be executed. The repetition of the word מות refers to death by human tribunal as well as by heavenly forces. The reason Avimelech used the word "whoever touches," was to warn his subjects that even conduct for which Gentiles normally are not punishable by death would become capital offences in this instance (compare what we have written on Genesis 20,4).