en_tn/1ki/16/20.md

the treason that he carried out

This treason refers to Zimri's plot to kill Elah, the king of Israel. The full meaning of this statement can be made clear. AT: "how he plotted against King Elah" or "how he killed the king of Israel" (See: rc://en/ta/man/translate/figs-explicit)

are they not written in the book of the events of the kings of Israel?

This question is used to either inform or remind the readers that the information about Zimri is in this other book. This rhetorical question can be translated as a statement. See how you translated a similar phrase concerning Judah in 1 Kings 14:29. AT: "they are written in the book of the events of the kings of Israel." (See: rc://en/ta/man/translate/figs-rquestion)

are they not written ... Israel?

This can be stated in active form. AT: "someone has written about them in the book of the events of the kings of Israel." (See: rc://en/ta/man/translate/figs-activepassive)