Depends on what character I'm playing as.
If I'm an archer thief, then he broke into a noble's house and was caught rifling through the silverware.
If I'm playing a mage, then he accidentally killed his master when one of his spells went wrong.
Those are the two I usually play as, but I have a couple of others prepared.
A petty criminal who sold weak poisons as "health drinks".
An uncivilised barbarian who liked to smack serving girls on the rear as they passed. But one of them turned out to be a visiting Duchess.
I tend not to play as really evil characters, as I just can't get immersed in it. I guess I'm just too nice a guy! But just in case . . .
A scheming "Grand Visor" character, who has been steadily poisoning the king's mind until he was completely unfit for rule. I also killed off the true heir to the throne soon after birth. However, I left some incriminating evidence behind which was recently discovered. This lead to my arrest, trial, and sentencing.