Revealing mistake: When Hightower is in the Monster Truck you can see that a white stuntman is actually driving it in one of the shots.
Continuity mistake: When Hightower emerges from the pile of rubble he has dust on his shoulders and arms, but when he walks up to the bad guy the uniform is as good as new.
Answer: Because they found jewelry from the last crime in his office. That's why he was shocked. They may be friends, but he knows he can't ignore evidence even for a friend.
lartaker1975