just some random thoughts:
Lucy and Howard were married, as were Alicia and Charlie.
Alicia was Howard's sister.
edit: there is a problem with this; each person slept in his/her own room.
But perhaps the hotel only had 1-person rooms.
While Howard was running the place, the actual 'owner' of the hotel was Alicia.
Alicia visited the place to find why Howard could not attract as many visitors as it used to do.
Howard always said that it was Alicia's fault, as she was almost never there.
That night, Howard got so frustrated he eventually ended up killing Alicia in her sleep,
in a desperate attempt to save the hotel.
While she was looking for her keys, Lucy realized it must've been Howard that killed Alicia
Not wanting to share her life with a murderer, but neither wanting to betray her husband, she ended up killing herself.
After accusing you, Howard found that, at some point, Charlie had to realize Howard was the murderer.
It might take an hour, a week, or 5 years- but he'd be accused of the murders.
So Charlie had to go.
Going over what happened, Howard suddenly comprehended what happened-
he killed his sister and her husband, his wife commited suicide.
To prevent an 'unsolved mystery' that would prevent the hotel from ever getting visitors,
he decided to have the person already accused being found guilty.
He silently slipped the master key under the door of the basement,
before going back to his office.
He locked his office with the 'normal' key,
opened -out of habit- the cupboard to hang the key back.
But at the moment he moved the key into the cupboard,
he realized he was about to sit down in his chair- not to actually commit suicide.
So he dropped everything in his hands (the key being on the bottom of the cupboard),
took a rope out of his office drawers,
attatched it to the ceiling, and knotted it.
He used the cupboard to climb up, stepping on the key, causing it to move a bit. (the key pointing out of the cupboard at this moment.)
more random thoughts:
-the witch is related to Howard.
-The witch has, as such, a (copy of the) master key.
-The witch could either be a mentioned or not a mentioned person in the story.
-If mentioned, Bill could have killed Charlie and Howard before going to the police
-Charlie could've been devoured by otyugh's, zapped by psions, or drowned in a flooding.
He could also be still alive, but having killed the non-mentioned witch.
