“That’s when the sender expected it to reach me,” declared Cardona, “but I got in ahead of him.
“The post-office authorities sent that letter down to headquarters at eleven o’clock last night. They were looking for it, and they got it. Where do you think it came from?”
“Where?”
“From the mail box in the Redan Hotel!”
“What!”
The exclamation was uttered by Weston and Biscayne in unison. Cardona nodded.
“Sure enough,” he said. “The killer is somewhere around the hotel. We’ve been on the job up there all night — quizzing guests and watching the place. But we haven’t got to first base.
“All we know is that the dead man in Harshaw’s apartment had been staying at the hotel for five days. He registered under the name of Howard, or Horace, Perkins.
“You can’t tell which from the way he scrawled his name on the register. That’s an alias, of course.
“He brought the collapsible ladder in with him in the suitcase. He must have gone to 918 — the room under Harshaw’s study — on the night that the old man was killed.