It can be made clear what the purpose of hanging him was. Alternate translation: "killing Mordecai by hanging him" (See: [[rc://en/ta/man/translate/figs-explicit]])
The gallows was a structure that was used to kill people by hanging them from it. See how you translated "gallows" in [Esther 5:14](../05/14.md). Alternate translation: "the structure Haman set up for hanging Mordecai" (See: [[rc://en/ta/man/translate/translate-unknown]])