If the key is rotating fully to the lock position then it is going to need the door panel off to see what is what.
Has it ever worked from the key either side ?
I found on my cos someone (previous owner) had disconnected the short rod that goes from the key barrel to the lock mechanism itself, both sides, so I did not need the £10 worth of door locks I bought, should have looked first!!
I think they do this to help stop theft.
tabetha