Continuity mistake: During the flashbacks of the abusive father's childhood his own father's shirt sleeves go back and forth from rolled up to just unbuttoned.
Revealing mistake: When The Hulk tosses the abusive father across the gym his blond hair looks fluffier and darker, indicating it's a wig on a stuntman.
Answer: The Hulk is accused of killing Dr. David Banner and Dr. Elenia Marks. After the lab explodes, McGee sees the Hulk emerge carrying the body of Dr. Marks, so he assumed the creature is guilty. It was McGee who caused the explosion. After following the trail of evidence of the Hulk to the lab, he hides when David and Elania arrive. In a darkened storage closet, he knocks over a bottle of flammable liquid. He confronts them, then is forced to leave by Banner, who says, "Don't make me angry, you wouldn't like me when I'm angry." When Banner reenters the lab, it explodes, caused by the Hulk when it went on a rampage trashing the lab, causing many electrical systems to catch fire, thus igniting the flammable liquid.