Why you need a locksmith ?
Well, that is a very good question.
A locksmith will know how to open a door, non destructive and destructive way. Of course destructive way doesn’t mean taking the door down from the frame. Just damage the key hole and manually remove pin by pin out and at the end rotate the inside lock. This need to be done by a someone who knows what is doing, a locksmith. Because the door needs to be untouched or the gearbox to stay untouched.
Obviously the non destructive way is the one wich everyone wants but depends of type of lock.
So don’t damage the frame or the inside lock. Call a locksmith, will save you some time and a big headache.