Matthew Poole and continuators on Jeremiah 41:18

18 Because of the Caldeans; for they were afraid of them, because Ishmael the son of Nethaniah had slain Gedaliah the son of Ahikam, whom the king of Babylon made governour in the land .

Here was one slain whom the Conquerour Nebuchadnezzar had made Governour in the Land of Iudah, and it was but reasonable for them to think that Nebuchadnezzar would take the affront done to himself, he being constituted Governour by him, and though Iohanan had nothing to do in that murder, yet he did not know but that the King of Babylon being ignorant of any parties amongst the Jews, might look upon them all as guilty who were Jews, and revenge Ishmaels blood upon all the remainder of that Nation, he therefore chuseth them an habitation for the present, from whence they might in a short time go down into Egypt, which was Iohanan's design as we shall read in the next Chapter.