Alma 25:4

and among the Lamanites which were slain, were almost all the seed of Amulon and his brethren, which were the priests of Noah, and they were slain by the hands of the Nephites;

Most of the Lamanites who died were children of Amulon and his brothers. They had been priests of King Noah. The Nephites killed them.

Among the Lamanite dead were nearly all the descendants of Amulon and his gang—the corrupt priests who once served King Noah. They fell in battle at the hands of the Nephites.