Emory Stewart was the murderer in "The Puzzler in the Pit".
After his parents died in a car accident a couple of years ago, Emory discovered that he was adopted while going through their paperwork. Although he initially reacted badly, receiving a couple of DUIs, he eventually calmed down and began to research his biological father, Lawrence Brooks, famous for his exceptional work on crossword puzzles.
After conducting extensive research on Brooks, officially for a book he was writing, Stewart made contact with his biological father directly and asked for a meeting. They arranged to meet in a café the following day, but Stewart waited for over an hour and Brooks never showed up. Hurt and upset, Stewart ran into Brooks while walking home, only for Brooks to express complete ignorance of the meeting or even who Stewart was. Outraged at this perceived rejection, Emory began to fight with his father, culminating in Stewart pushing Brooks with such force that he fell back and broke his neck. Panicking at what he had done, Stewart took Brooks' body to a nearby fracking plant and dumped it in a pit, dumping additional acid on the body to obscure what he had done.
During the subsequent investigation, the team were able to confirm that Stewart was responsible for the death. In the final interview with James Aubrey, Stewart was horrified to learn that the reason for Brooks' ignorance was that he had been suffering from Alzheimer's, which meant that he had genuinely no idea who Stewart was during the conversation.