Of people who participated in filming, is very interesting, all of the family has very restless movements. Such things say more than words.
The widower himself first makes a statement that he never did anything illegal... And that adds something in lines like he did it, but was never caught. It's not a funny thing to say considering that he was a suspect for killing his wife. Also, he insisted on not being in clubhouse, even though that would be alibi for him, but then, Maria Martha's sister and her husband would lose theirs, being that maid of theirs said everyone was gone by 6pm and she cleaned up the table in living room. That would put them easily on the scene in the murder time-line.
As for the motive... Who knows, it could have been anything, people are very versatile in that department, especially when rich and bored.
This cover-up they made was a crime on its own, I can't imagine being in a mindset like them to think that everything will magically disappear because they destroyed the scene and because they feel that in their rich little community, anyone and anything can be bought.
Like already said in the documetary:"If there is no justice let there at least be truth."
Review of Carmel: Who Killed Maria Marta?
