TT #50 · Parashas Noach · Fourth Aliyah · Passuk 9:5
…and of man…
Torah Temimah notes the Yerushalmi reading that a Ben Noach may be executed on his own admission.
English: “And of man” — this teaches that a Ben Noach is executed even on the basis of his own admission.
Custom (self-incrimination accepted in Noachide law).
Unlike Israelite courts, a Ben Noach’s own confession can suffice for capital liability (per this reading).