The stableman at the inn was the only witness to the murder.

The correct answer is: B. Ostler

An ostler is a person who takes care of horses at an inn or stable. They are responsible for feeding, watering, and grooming the horses, as well as cleaning the stalls. Ostlers may also be responsible for taking care of the guests’ luggage and for providing transportation to and from the inn.

The other options are incorrect because:

• A butler is a male servant who manages the household affairs of a wealthy family.
• A jockey is a person who rides horses in horse races.
• An imposter is a person who pretends to be someone they are not.