3 After the kingdom was firmly in his control, he executed the officials who had murdered his father the king.

Read 2 Chronicles 25:3 Using Other Translations

Now it came to pass, when the kingdom was established to him, that he slew his servants that had killed the king his father.
And as soon as the royal power was firmly his, he killed his servants who had struck down the king his father.
When Amaziah was well established as king, he executed the officials who had assassinated his father.