In the seventh month, however, Ishmael son of Nethaniah, the son of Elishama, who was of royal blood, came with ten men and assassinated Gedaliah and also the men of Judah and the Babylonians who were with him at Mizpah. (NIV)
But in the seventh month Ishmael son of Nethaniah, the son of Elishama, of the royal family [so having a claim to be governor], came with ten men and smote and killed Gedaliah and the Jews and the Chaldeans who were with him at Mizpah. (AMP)
But it came to pass in the seventh month, that Ishmael the son of Nethaniah, the son of Elishama, of the seed royal, came, and ten men with him, and smote Gedaliah, that he died, and the Jews and the Chaldees that were with him at Mizpah. (KJV)