To the Imperial Legion,
Who I am is less important than what I know - suffice it to say that I am no friend to the so-called Stormcloak rebels.
Through various means it has come to my attention that [steward's name] had a rather embarrassing indiscretion in [his/her] past. I also happen to know that [victim's name] is foolishly keeping evidence of this affair.
Should you locate that evidence, you might be able to "persuade" [him/her] to help your fight in [hold name]. If forced to chose between his dislike for the Empire or [his/her] love for [himself/herself], [he/she] will most assuredly chose the latter.
A loyal citizen.