He had become the tenant of Mr. Longestaffe's house, and at the same time had only been the joint tenant of Mr. Longestaffe's study,--so that Mr. Longestaffe's papers were almost in his very hands. To pick a lock was with him an accomplishment long since learned. But his science in that line did not go so far as to enable him to replace the bolt in its receptacle. 
At the time, he was the joint tenant of Mr. Longestaffe's study; and he had long since learned to pick a lock, though he could not then relock it. 