Another theory on who sent the tapes - more than one involved!

(Spoilers)
One of the tapes was shot inside Majid's apartment, so that tape's production had to have involved Majid and/or his son.

We only know for sure that Georges and Majid, and presumably Majid's son and Georges' mother (if Georges' story as told to his wife is to be belived), knew about the story of Majid bleeding; and Georges apparently didn't tell anyone we see in the film about it until he ultimately told his wife. Georges' mother is old and feeble and doesn't seem like a likely suspect (both from how she interacted with Georges and from the fact that we were shown so little of her in the film). It's possible that Georges' mother could have worked with an accomplice, but that seems very far-fetched. Majid's denial of knowledge of or involvement with the packages seemed very sincere to me; especially when you consider that he had nothing left to lose, so why would he not have just admitted his involvement as his final act rather than go on lying to his grave? That leaves Majid's son as being very likely to have been directly involved.

The question is whether Majid's son did it all by himself.
I think the way the film was developed makes that unlikely.

First, why were there so many intercut scenes of Pierrot? The very first scene we see right after the dinner scene with Georges, Anne, & Pierrot at the very beginning is a scene of Pierrot swimming laps in the pool. Why was that scene there? We never really get any kind of explanation for the significance of that scene.
Second, why did Majid's son meet with Pierrot in the final shot? What reason did they have for having any kind of acquaintanceship?
Third, what led Pierrot to suspect that his mother was having an affair?
Fourth, it has been mentioned in another thread that the camera equipment used to make the recordings must have been expensive--presumably too expensive for Pierrot or Majid's son to have access to such a camera. I think that suggestion is a bit too presumptuous. We really don't know anything about Majid's son--what kind of work he does and what kinds of acquaintances he has. Why couldn't he have gotten access to such a camera somehow? And we know that Pierrot's swim team mates had family or friends who have cameras that they used to record one of the swim meets. So I think either of them could have gotten access to a camera. Pierrot also has friends that we know virtually nothing about; perhaps they could have helped him install a camera.

I think the most likely explanation, given the way the story was revealed and given the film editing choices, is that Majid's son worked with Pierrot to record and send the tapes and letters. I think Majid's son came up with the scheme and convinced Pierrot to help him. Maybe he planted the suspicion in Pierrot's mind that Anne was having an affair, which would have provided a motive for Pierrot to want to film the front of the family home. Pierrot may not have known all that was going in--the postcard sent to the school, for example, may have been Majid's son's doing alone.