Among the research and paperwork on a table regarding H. H. Holmes and his crimes is a black and white photo of a dead woman. However, the photo is not of one of Holmes' many victims, it's of Elizabeth Stride, one of Jack the Ripper's victims.
When Dean shows up with a concrete truck to bury Holmes, it appears, but not shown, that the goal is to fill the underground space completely. They would need dozens of loads to complete the job. Concrete trucks can carry between eight and ten cubic yards.
In real life, Holmes's Modus Operandi was nothing like the behavior portrayed by the ghost in this episode.
When Dean and Jo are searching the building's halls, a green screen can be seen through a window multiple times.