Revealing mistake: When Adler fights with David close to the detonator just before his second transformation, the shots are filmed too close. It makes it really obvious that a stuntman is replacing David for most of the fight.
Continuity mistake: When Adler moves David into the barrel and loads him into the truck before his first transformation, David's head is at the bottom of the barrel. But when the Hulk emerges from the barrel he is already standing on his feet.
Continuity mistake: When Mike is on his balcony with Linda, we see that he is talking to 12 workers. But, in the next shot, a 13th worker wearing an orange hat and an olive green jacket magically appears almost completely to the right. However, when the 12 workers leave the area, the 13th worker cannot be seen anywhere.
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.