When one of the Marshalls is being questioned whilst sitting in back of an ambulance. He says that before he knew it, the handcuffs were off. But in the tracking shot within the SUV, Cooper's hands are shown to be separate and in his pockets the entire time.
When Cooper (J.R. Ramirez) takes out 3 U.S. Marshalls in the SUV, the Marshalls in that shot were terribly irresponsible. When someone is transported by the U.S. Marshall Service, they are not unrestrained. Standard restraints include Handcuffs, a Waist Chain, and Leg Irons. Further, they are kept in a secure section of a vehicle. More for someone they believed to be a threat. In other words, this would not be possible.