And, after he first mentioned the exploit, and before he achieved the award, the AT&T lawyers made him say publicly that he didn't really do that.

Where can we find records of him stating that this never happened?

I am unable to locate it now.

It seemed very weird at the time--the AT&T lawyers making him deny what he had done.

And it is possible that the denial was about the general release of the exploit, rather than whether or not he really did it. My memory could be slightly off for events back that far ago.

It was a minor industry rag and the story was published shortly after the hack was announced. It might have been the same paper that Dennis Ritchie told of auditing the behavior of Coherent and saying publicly that it was definitely not a clone. I think the lawyers were upset about that as well.