It is more than probable that he was clean-shaven during his absence, or up to about two weeks ago.

Then, in order not to emphasize his altered appearance when he came back, he permitted the mustache to grow again." "But what does all this mean ?" inquired Greig.
"It means that Whitmore was not away on a business trip," answered Britz.

"The statement of Beard to visitors at the office was a blind.
Business men don't shave off their mustaches when starting on a business trip.

No, Whitmore was away on a matter intimately associated with his murder.

And, by means of the photograph we shall discover where he was and what he did.