I framed one of my player's characters for murder once.
In the middle of a conversation with a minor noble from the character's home area, said noble suddenly began coughing and died clutching at his throat. Everyone in the room saw the PC hand the noble a glass of wine shortly before this happened, and everyone knew there was bad blood between the two of them.
Surrendering to the authorities would have lead to a quick trial with predictable results, so the PCs fled the scene after a brief scuffle with the nobleman's guard. The one accused of murder was able to find a patron powerful enough to keep his neck out of the noose for the moment, and they began an investigation. After some intimidation and diplomacy and a little skulduggery they were able to determine that his Lordship had been poisoned with a two-part toxin; one part in the food and one in the wine. This explained why none of the other people in the room (who also drank the wine) were killed.
More clues were unearthed, eventually pointing to the captain of the dead noble's guard. He was well known to be an unacknowledged bastard son, but as the dead nobleman had no heir he expected to be acknowledged and confirmed as his successor. Alas for his ambitions, it turned out the dead man was about to announce his betrothal to a young (and presumably fertile) member of a powerful noble family. The bastard saw his inheritance slipping away and decided to take drastic measures.
Once the PCs figured this out (a process that involved Speak with Dead and a midnight Invisible Stalker ambush in the rain-slick streets) they were able to find corroborating evidence (documents acknowledging the murderer as the dead man's son and naming him as his heir, essentially removing the taint of bastardy) all that was left was to present this information to the magistrate. Role-playing the trial was a lot of fun but also a bit of a pain in my neck as I had to take on a lot of roles in rapid-fire, in retrospect I wish I could have recruited a few outsiders, but anyway -
When all was said and done, the murderer demanded trial by combat, and the PC originally accused of murder managed to defeat him by the skin of his teeth. It made for a great and dramatic conclusion. My players all loved it.