Why officers in “The valley of fear” were curious and suspicious

Holmes soon deciphers the message regardless, and discovers that it warns that Douglas of Birlstone is in imminent danger. The two are soon visited by MacDonald, a policeman friend of Holmes, who informs them that this same Douglas has been murdered.

Upon inspection of the dead man, it is revealed that he has been killed with a sawed off shotgun, an American weapon. Beside the disfigured body lies a card inscribed 'V.V. 341'. Other clues in the room include a bloody footprint on the windowsill, a missing dumb-bell, and the fact that the man’s wedding ring is missing.