Just a Pretty Face?
We don't know a lot about Devereaux, except for the fact that he's a movie star with money trouble. And Charnier, like a cat with a mouse, pounces on him, using his celebrity cache to get the drug car from France to New York. When the press scrum asks Devereaux why he would take a boat rather than a plane, he's ready to answer, saying,
"The next several weeks will be very difficult and the middle of the ocean is the only place where the telephone isn't ringing all the time."
That seems to satisfy everyone, and Charnier has precisely what's needed.
But Devereaux isn't a hardened criminal like Charnier or even Sal. So when he has to make a case for getting back the drug car at the police lot, he loses his appetite for the caper, and tells Charnier he's out. Unfortunately for him, it isn't soon enough, and he pays for his involvement by serving four years in the Federal pen.
For the film as a whole, Devereaux is perhaps the cautionary tale, just a rube looking for some kind of shortcut and getting in too deep. Like Mulderig for Popeye, Devereaux is collateral for Charnier, who conveniently disappears just after the bust.