One Deathless Hour — Roger Ormerod

When the time indicated by the clock shattered by a fatal bullet is the same as the time the victim was apparently committing a murder somewhere else, detectives David Mallin and George Coe are acutely suspicious. They find themselves at opposite ends of an alibi and conclude that their client must be the murderer. After all, if the shattered clock is an attempt to fake an alibi, then it must have been a marksman's shot, and their client, Victor Abbott, happens to be a marksman.