You are not the murderer; you were outside spying on Prince Maroon and Miss Scarlet for the better part of the evening.  This provided some interesting information – they claim to have been out there looking at horses, but you doubt it, as they were completely nude -- but won’t work as an alibi because no one can but confirm it.  In order to get permission to work on the case (and to get the fat reward for finding the killer), you have bribed the cook to swear that you were in her room copying recipies for most of the evening.