My GUESS is the link between the lock cyl and latch broke or came off. About the only way to get it open without destroying the lock and trunk lid (by pulling the lock out with a slide hammer) is getting to the back side of the latch through the inside. There's a slot in the latch that you can turn with a screwdriver from inside the trunk. If there's a tail panel trim cover, it'll have to come off,,,,,,,,,,,,,,,,,somehow. Having the trunk full will toss a monkey wrench in the procedure though.