You are referring to the final (10th) plague of Egypt in Exodus 11,12.
I see no mention of "henchmen", but rather God Himself ("I"/"The Lord") as the agent of death. All who were covered by the sacrificial blood of the Lamb were spared. But the hard-heartedness of men still refuse the passover gift.
God's Point (since you didn't explain it): God is perfectly within His rights to kill us all for we deserve death (wages of sin). Thank God, He provided a way out, as He did then.
The story that I read had angels doing to wet work.
I think the Angel of Death was sent as payback for the time when Pharoah killed the baby boys of the Israelites, and also to let Pharoah know that God has total control of who lives and who dies and when.
But Heavenly Father is engaged in a long battle with Satan and his minions, and such battles have real casualties, some innocents, just like any war. All that happens is necessary for the salvation of as many souls as possible.