If he sends messages to that person it means that he has received a pigeon or pigeons from that person within a week.

And how were these pigeons shipped?
In all probability, by express.

So, gentlemen, you see there ought to be a record in the express offices, which would give us the home town, even the name and address, of the person who now has the diamonds in his or her keeping.

Is that clear to all of you ?" "It is perfectly clear," commented Mr.Laadham admiringly, while the German nodded his head in approval.
"And that is the clew we are working on at the moment," the detective added.

"Three of my men are now searching the records of all the express companies in the city--and there are a great many--for the pigeon shipments.