Why would they want to frame the husband and kill her best friend?
Excellent thriller, but these two actions doesn't make sense.
If Neuville wanted to get Margot, Alex (her constantly trying to contact him) was his best lead. Why would he want to frame him (the gun) and cut him off?
And why would they kill Margot's best friend -- just because she couldn't tell where she was?? Nobody knew, so -- errm, maybe let's kill everyone? There's Alex with that online chat with her, why first go to her friend? Unless, their plan WAS to frame Alex, but there's no real motive.