return to his home, after a visit to the goldsmith in question.
He had a short interview with Chief of Police Bauer, who finally
gave him the golden bullet and the keys to the apartment of the
murdered man. Then the two went out together.

An hour later, the chief of police and Muller stood in the garden
of the house in which the murder had occurred. Bauer had entered
from the Promenade after Muller had shown him how to work the lock
of the little gate. Together they went up into the apartment,
which was icy cold and uncanny in its loneliness. But the two men
did not appear to notice this, so greatly were they interested in
the task that had brought them there. First of all, they made a
most minute examination of the two doors which had been locked. The
keys were still in both locks on the inside. They were big heavy
keys, suitable for the tall massive heavily-paneled and
iron-ornamented doors. The entire villa was built in this heavy
old German style, the favourite fashion of the last few years.

When they had looked the locks over carefully, Muller lit the lamp
that hung over the desk in the study and closed the window shutters
tight. Bauer had smiled at first as he watched his, protege's
actions, but his smile changed to a look of keen interest as he
suddenly understood. Muller took his place in the chair before the
desk and looked over at the door of the vestibule, which was
directly opposite him. "Yes, that's all right," he said with a
deep breath.

Bauer had sat down on the sofa to watch the proceedings, now he
sprang up with an exclamation: "Through the keyhole?"