I turned to go, but the door had been locked from the outside.

The door could not be locked from the inside or outside.

The door to his room was locked from the outside.

The door to his room was reported to have been locked from the inside.

But there is nothing to show if were locked from the inside or the outside.

It was locked from the other side and had to be worked open, too.

The door to the hall was locked from the outside.

It was locked to the outside but not from the inside.

He tried the door of the study and found it locked from the outside.

Very probably, he had closed the door and locked it from the other side.