Gedaliah is assassinated
Johanan warned Gedaliah that Ishmael was planning to kill him. Gedaliah would not believe it, and Ishmael killed him.
Key passages
2 Ki 25:25

But it happened in the seventh month that Ishmael the son of Nethaniah the son of Elishama from the offspring of the kingship came, and ten men with him, and they struck down Gedaliah so that he died with the Judeans and with the Chaldeans who were with him at Mizpah.

Je 40:13–41:3

And Johanan the son of Kareah and all the commanders of the armies who were in the open country came to Gedaliah at Mizpah and said to him, “Are you at all aware that Baalis, the king of the Ammonites, has sent Ishmael the son of Nethaniah, to kill you?” But Gedaliah the son of Ahikam would …