What do John Berry and George Wilson witness after they follow J.D. Randall and Peter Randall along the coast?

Undetected, John Berry and George Wilson follow J.D. Randall and Peter Randall along the coast. They watch the brothers pour gas in the front seat of Peter Randall's car, a vehicle that Peter claimed had been stolen. They then witness the Randalls shoving it over a cliff, where it explodes.