Why would the Victorians have found "The Tell-Tale Heart" particularly disturbing?

The Victorians were particularly concerned with duplicity and deception and a person's ability to be secretly sinful or suffering from "madness" while tricking the world into believing that they were morally upright and/or mentally sane.  The thought that one could be fooled by such a person and exploited, injured, or otherwise harmed, was both a frightening and titillating prospect.  Therefore, they enjoyed fiction that focused on characters who enacted this kind of fraudulent behavior because...

The Victorians were particularly concerned with duplicity and deception and a person's ability to be secretly sinful or suffering from "madness" while tricking the world into believing that they were morally upright and/or mentally sane.  The thought that one could be fooled by such a person and exploited, injured, or otherwise harmed, was both a frightening and titillating prospect.  Therefore, they enjoyed fiction that focused on characters who enacted this kind of fraudulent behavior because they found such persons so disturbing.

The narrator of "The Tell-Tale Heart" most definitely qualifies as duplicitous.  He says that he "was never kinder to the old man than during the whole week before [he] killed him."  By day, the narrator appears to be friendly and loving to the old man (though his relationship to the old man is never clarified: the old man could be his father, a roommate, etc.), but, each night, he spends spends hours practicing the movements he will use to kill the old man when the conditions are just right.

Further, after he's committed the murder, he is such a powerful dissembler that he manages to fool the police officers who came to investigate the scream his neighbors reported hearing.  The narrator says, "The officers were satisfied.  My manner had convinced them."  It isn't until his own paranoia and delusion drive him to confess that they have any sense that he is guilty.

Such a powerful deceiver, one capable of inflicting such damage without scruple, one who actually believes that his actions are justified, would have been both particularly interesting and particularly frightening to Victorian readers.