[LockDoc]

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You are pretty much out of luck on it if you don't have the key. Be sure and spray the inside of the lock with a good penetrating oil and try your ignition key. Insert and remove it a few times to loosen up the tumblers. If the key will slide into the lock it may work. (don't force it)

Even if you can get to the latch bolt from the back you can't retract it because the locking system has a dead latch that keeps the latch bolt from retracting until the key is turned to the unlocked position. There is a spring clip that holds the lock cylinder in the door. If you could get to that and slide it off, the lock cylinder will come out. (See picture below) If you go that route be sure and spray the clip before trying to remove it.

In the picture the lock is in the unlocked position. When locked, the tab turns and blocks the lock bolt so it can't be retracted when the handle is pulled.