Jeremiah 41:3

Ishmael also slew all the Jews that were with him, even with Gedaliah, at Mizpah, and the Chaldeans that were found there, and the men of war.

Ishmael slew all the Jews who were with Gedaliah at Mizpah. Along with them he slew the Chaldeans that were found there and the men of war. This killing was the treacherous slaying of Gedaliah, the governor appointed over the poor remnant.