H.H. Holmes is notorious in popular culture for being a vicious serial killer who built a hotel in Chicago that was supposedly filled with hidden gas chambers and other murder contraptions. An article I recently read online claims that much of these stories were fabricated by newspapers covering the case. It also states that while he definitely murdered several people, the "Horror Hotel" never truly went into operation.

So what historical evidence do we have about Holmes and his criminal activities? How trustworthy are the sources dealing with his case?