It is hard to believe a French researcher, traveling from France to the US, was in possession of confidential information he retrieved from a US national lab. It is harder to believe they didn't arrest him for this.
Not at all, it's much more believable than the original story. Traveling scientists frequently work at national labs.
>It is harder to believe they didn't arrest him for this.
Nondisclosure agreements are civil in nature, not criminal.