Kahn's rear door had been opened with false keys and left ajar.

Then Phin Drayne stole back to the junk shop, while Stevens, whose voice could not be recognized over the wire by Dick, sent the message.
Next, back to where he could watch the alleyway, hurried Stevens, and hid.

Stevens saw Dick Prescott slip into the alleyway, then go inside the store.

That was enough for Stevens, who had slipped back and into the drug store once more, getting the police station on the wire and 'phoning to the chief that Gridley's burglars had just entered Kahn's through the rear door.
Only a block and a half from Kahn's was the police station.

Almost immediately the officers were on the spot, stalking---Dick Prescott.
But, at the time when Dick left his own home and went down the street so hurriedly Dave Darrin had been sauntering along, to call his chum out on their nightly quest for "The Blade." Seeing Dick move so swiftly, Darrin concluded that something most unusual was about to happen.