Behind the séance is one of the most practically important — and most misapplied — principles in recordkeeping: unwitnessed and unexplained incidents are still recordable. Employers regularly convince themselves that if nobody saw it happen, or the employee 'can't explain how,' the case is somehow optional. It is not, and the ghost proves it.
The work-relatedness presumption in 29 CFR 1904.5(a) attaches to injuries 'resulting from events or exposures occurring in the work environment.' An employee at the bottom of a ladder with a broken wrist is the result of an event that occurred in the work environment. Nothing in Part 1904 requires a witness, a root cause, or an accepted physics of what happened — the exceptions in 1904.5(b)(2) are a closed list of nine, and 'unexplained' is not on it. If the injury involves medical treatment beyond first aid, days away, or another 1904.7 criterion, it goes on the log within 7 calendar days of receiving information that it occurred (29 CFR 1904.29(b)(3)).
As for the perpetrator: the OSH Act imposes its enforceable duties on employers (OSH Act §5(a)), and citations attach to employers — not to coworkers, customers, weather, wildlife, or the restless dead. But here's where the joke earns its keep: an 'unexplainable' fall from a ladder is exactly the moment to inspect the actual suspects. Was the ladder defective (29 CFR 1910.23(b)(9) requires ladders be inspected before initial use in each work shift, and (b)(10) requires defective ladders be tagged and removed from service)? Wet rungs? Overreach? Improper setup? In incident investigation, 'a ghost did it' is a data point that your investigation isn't finished.
The takeaway: record the case, investigate the ladder, and remember that the log is a census, not a courtroom. Ghosts have never once been the root cause. Loose ladder feet have been the root cause thousands of times.