I'm wondering about Henderson. For some reason I think he would be more subtle, and would talk in circumlocutions that could be misunderstood by anyone who is viewing the closed circuit TV footage of Clark and Henderson's interrogation room.
I could see Henderson hinting at it, Clark reluctant at first, Henderson coming out a little bit more, and then Clark, well, not denying it, in such a fashion that Henderson would consider it a confirmation. But nothing would be said overtly.
Sorry - this is just the way I picture Henderson. Given that they are in a prison, and there is lots of surveillance, I'm not sure that Clark would be so open with his admission.
Just my $0.02.
