True?
There a some websites that indicate the story to be -at least- based on some actual persons or events but are there any documents (court records, newspaper accounts) that back up any part of the story?
Leroux was inspired by the legend of a man who lurked in the depths of the Paris Opera house. I believe the characters are fictional though, as is the story about Christine and Raoul and the Phantom inspiring people's music.
As with any legend, the mysterious guy lurking in the Opera house might have been blamed for accidents that occurred, but that doesn't mean there was any truth to that. As far as finding "evidence" that the legend was real, I think that's hopeless. There are likely newspaper articles about it, but that wouldn't prove the veracity of the legend because newspapers can write about legends and myths (newspapers report sitings of bigfoot).
It wasn't really the legend of a man who lurked in the depths, it was more just like ghost stories. Most theatre-type places like an opera house has them.
shareActually, I think this was a specific legend about a guy roaming around in the depths of the Parison Opera house. At least that's what the accompanying commentary piece in my book says. But yeah, I bet most of these types of places have ghost stories - and it could be that something was lost in the translation or that the story Leroux wrote, about a man lurking in the depths of the Opera house has sort of taken over the ghost story that once existed.
I suppose someone could go back and research what legend existed before Leroux wrote his book, but that person would have to be fluent in French and have access to archives.