Ok she didn't drink the blood, rumors were she bathed in it. Not sure if it's true or not. Either way, this was one messed up lady and this is what we know about her 400 years later, think about what truths have been lost since then....
http://www.trutv.com/library/crime/serial_killers/predators/bathory/countess_1.html
The thing about Elizabeth Bathory is that we don't know how much of it is speculation (the bit about bathing in blood is probably false) and how much of it is true. At the time of the trial several witnesses went forth to testify that their female relatives and acquaintances had disappeared and reportedly some men who were sent to her castle found a dying girl and saw her torture chambers. At the same time, Elizabeth's conviction was very politically convenient and many of the people who testified could have been attempting to make sure that they were on the "right side". Maybe she really did all of it but everyone overlooked it until they needed a reason to convict her. Who knows.
On-topic: the fact that they're not releasing the files is really suspicious. Of everyone's ideas here these is my :twocents::
- Ripper tours are a source of money - I don't know if the information they had on file would end the mystery, if they had a sure suspect then they would've arrested him back then. It seems more likely that people would still have to speculate but with more information available to them.
- Incompetence - I don't see this. Maybe the SY made mistakes but everyone is aware that in the 1800s, forensics was hardly what it is today and if they messed up on a case over 100 years ago it doesn't mean they still regularly mess up. I doubt it would have an effect on their image.
- Vanishing files - Yup, this one I can believe. It sucks but unless people had access to those files to begin with nobody would know that anything was missing so they could release what they have.
- Protecting people - Didn't the original article on pg. 1 mention that they were trying to protect informants? Informants wouldn't have been that high-up in Victorian society and whoever they reported wouldn't go after them now. HOWEVER, an important informant could have been someone with ties to high-society, tied in with something that would have been very inconvenient for SY or someone else, or perhaps a relative of someone who is currently important and powerful. If you're a CEO or a politician the last thing you want is to tell the world that your great-great-grandfather was a criminal. If they're trying to protect the identity of the murderer the only way they'd still care is if it's someone linked to an important family, not necessarily the royal family but another upper-class one.