In case you need a refresher, after Thaddeus Sivana, against the wizard Shazam’s protests, stole the Eye of Sin from the Rock of Eternity and became the new vessel for the Seven Deadly Sins, he traveled to Sivana Industries to confront his father and brother.
Now that he had the power to exact revenge, Thaddeus tossed Sid out the window and had the Seven Deadly Sins murder Mr. Sivana and everyone else in the room.
Both of them had been emotionally abusive towards Thaddeus growing up, with his brother, Sid, blaming him for the accident that paralyzed their father.