Nice, but why...
... didn't they know the rollercoaster from the opening scene was sabotaged? The rails were blown using a bomb! It must have left some traces, even for 70's CSI to recognize.
... didn't the FBI agent in the tower notice the young man? He was wearing a clearly visible earphone in his left ear (must have been a rarety in those days) while contantly observing Calder through his OWN binoculars while standing right next to large fixed binoculars from the park.