A lot of time passed between Fantomas taken Juve and Fandor out of jail and the police finding out that they escaped. But just right after that, the police locate them with the helicopter, even though they did not know which way they took and which car they used.
Supposedly Fantomas is wearing Fandor's mask, however he does not remove it completely to put on Juve's mask.
Fandor and Juve don't see Fantomas jump out of the locomotive, nevertheless they continue the chase and they arrive to the beach just after Fantomas take his boat.