When you go to jail try pickpocketing the guard that usually walks by.

If he doesn't notice you take something take more until he notices you. He will attack you. Kill him whatever way you wish.

Run out of the jail and get arrested again. Serve your time then get arrested again. Keep getting arrested until you find that the dead guard is alive in the cell with you.

He should open the cell door. If you follow him you can attack him and he won't fight back.

Any way you can also walk out as if it were a jailbreak yet it won’t be counted as a jailbreak. Instead the game would just count it as if you were visiting a prisoner. You can take your things out of the evidence chest and go free with a bounty, yet the guards won't arrest you unless you talk to them or commit a crime.

Note: This does not always work.