We know they were following a script.
The French "scientists" stilted dialogue was English (with a Fransh accent, but of course!). And the "witness" was played by an English-speaking actor in some scenes, as were his neighbors). Incidentally, in the other scenes, the "witness" was not even speaking French, but some other language similar to Italian (I could actually understand him, it might have been Provecal. Of course it was a dramatic production, they didn't even make an attempt to disguise it. I tuned out when Inspecteur Clouseau arrived.
I'm sorry J, but the burden of proof is on you. If you can't believe David, believe me. You know I would never lie to you, n'est–ce pas?