"Why don't you prove that they are U.S. citizens."
Because MoMo is the only one here who CLAIMS he "talked" to them. He's the only one who ostensibly knows where they are from. There are only two reasons why he could not divulge that information:
1 > Because they do not exist and so he can't reveal the information.
- or -
2 > Because he's lying.
Actually, there's the third and most likely possiblity, and that is both 1 and 2 are correct.
In the absence of information to the contrary, since they are supposedly officers of a US public company, it's logical that they are US citizens. All lies to the contrary not withstanding. { 8^D