The maintenance guy *here be spoilers* !!!
One thing I've never understood, much as I like this movie:
Why on earth didn't that maintenance guy report what was going on? He says to Susan: 'I've seen how they do it', meaning he knows that those involved in killing the patients are using carbon monoxide, and how they are giving it to them in surgery. So why did he not call the police or report it to some other authority? Are we meant to surmise, perhaps, that Harris/others involved in the killings knew that the maintenance guy was on to them, and threatened to kill him if he called the cops? Therefore, did he tell Susan what was going on hoping that she would report and stop it without any risk to himself? I should say that I am autistic and don't always interpret things correctly, but I do wonder about this aspect of the plot.
Your mother darns socks in hell