Where was John Surratt on April 14, 1865 ?

[L Verge]

In Lincoln's Assassins: A Complete Account of Their Capture, Trial, and Punishment by Roy Chamlee the author writes:

"Surratt told his lawyers that he had stayed at the Brainard House in Elmira on April 13 and April 14. But when the lawyers searched for the crucial register, it could not be found. Their exhaustive efforts lasted several weeks. They questioned everyone connected with the hotel, but no one could find the register. Every other guest book before and after the missing one was available."

Any theories on what happened to the register that could have proven Surratt really was in Elmira?

Elmira was Copperhead country, so I suspect that the Brainard was a safe house and that "someone" in their employee deep-sixed it. Or, we might want to consider that the federal authorities had confiscated it so that there would be no proof that Surratt was there - thus damaging his testimony.