Jeremiah 41

Then Ishmael the son of Nethaniah, and the ten men who were with him, arose and struck Gedaliah the son of Ahikam, the son of Shaphan, with the sword, and killed him whom the king of Babylon had made governor over the land. Ishmael also struck down all the Jews who were with him, that is, with Gedaliah at Mizpah, and the Chaldeans who were found there, the men of war. vv.2-3

Read chapter 41
The threat of Ishmael killing Gedaliah from chapter 40 comes to pass here.  Ishmael son of Nethaniah was of the seed of David and must have thought he had more right to be named governor than Gedaliah who was named governor by the king of Babylon to those left after the destruction and captivity of Jerusalem.  So this jealousy and pride led to the murder not only of Gedaliah but to many men, women and children who were under Gedaliah's care.  Ishmael and the men with him had come to Gedaliah in deceit eating a meal together yet in this moment of hospitality and fellowship is when they attacked.  Just when this remnant of people thought this war with the enemy was over and thought they had nothing left to lose, some of their own people take their lives.  Luckily for those that were left alive and captive by Ishmael are rescued by Johanan who was Gedaliah's friend who had warned him of Ishmael and they go to dwell near Bethlehem and under the Babylonian administration. 
May we always be on guard to of the battle after the battle, especially among our own people.