The de la Pena diary is debatable, although evidence slowly builds that it is real. The collector that "found" it was less than credible. There are two manuscripts--one shown to be in de la Pena's hand, probably written at the time of the events. The second is not in his hand; apparently, it was written while he was in prison. He was too ill to write, so he transcribed it. Hands-writing experts seem inclined to think that it's the real thing for a number of reasons. But it's the one in doubt and it's the one that mentions the executions in one paragraph.
Some archeologists looked at his descriptions of landmarks and, with the use of satellite images and GPS systems, have located an area where he said a city was located (they found chards and it's today in the middle of a desert), a fork in a road the exact distance from the city like he noted and soldier-type relicts that would indicate troops had traveled it in the past. Pretty interesting stuff.
The name to remember is Jake Ivey. He is a man who has done decades of research and it was his findings that were plugged into a computer and developed into 3-D pictures. He discovered, for instance, that the north wall was 3 feet thick.