Explanation not psychologically apt. Also plot holes.<spoilers!>
How did Bosner manage to impersonate Leidner without being an archaeologist?
If Lousie was well off(at least her father was), Why did she not hire a personal detective to look into the letters when she thought she couldn't go to the police?
What about the acetone incident?
How could Bosner pursue his career (involving digs at various sites all round the world and intense study especially for him) and keep tab on Louise's personal life without any help?
If there were any help, wouldn't they be a threat to Bosner's plan(given they were not in on the murder plan)?
If they were in on the murder plan, aren't they accomplices and ought to be caught?
Other than that, Cristie posing as an amateur writer is quite amusing and is well thought of.
Would have been better if the husband had not been the murderer (too typical and unnecessary here). It would have been a better crime if Lavigny were Fred Bosner and Elmott Will Bosner.
Lousie would have been on knees for prayer before Lavigny and he could have struck easily. Elmott would have been responsible for keeping on the courtyard.