Esther 9:13 - Matthew Poole's English Annotations on the Holy Bible

According to this day's decree, i.e. to kill their implacable enemies. For it is not improbable that the greatest and worst of them had politicly withdrawn or hidden themselves for that day; after which, the commission granted to the Jews being expired, they confidently returned to their homes, where they were taken and slain by virtue of this private and unexpected decree. Haman's sons were slain before; now let their bodies be hanged upon their father's gallows, for their greater infamy, and the terror of all others who shall presume to abuse the king in like manner, or to persuade him to execute such cruelties upon his own subjects. This custom of hanging up the bodies of malefactors after their death was frequent among the Jews, and Persians also, as is well known.