Those who conspired against Joash were Zabad son of Shimeath the Ammonitess and Jehozabad son of Shimrith the Moabitess.

2 Kings 12:21
His servants Jozabad son of Shimeath and Jehozabad son of Shomer struck him down, and he died. And they buried him with his fathers in the City of David, and his son Amaziah reigned in his place.

2 Chronicles 24:25
And when the Arameans had withdrawn, they left Joash severely wounded. His own servants conspired against him for shedding the blood of the son of Jehoiada the priest, and they killed him on his bed. So he died and was buried in the City of David, but not in the tombs of the kings.

2 Chronicles 24:27
The accounts of the sons of Joash, as well as the many pronouncements about him and about the restoration of the house of God, are indeed written in the Treatise of the Book of the Kings. And his son Amaziah reigned in his place.

And these are they that conspired against him; Zabad the son of Shimeath an Ammonitess, and Jehozabad the son of Shimrith a Moabitess.