Can't stop thinking about this...
Whoever killed the daughter was close enough to her/ cared enough about her to drug her so she wouldn't realise what was happening, correct? But didn't give enough of a shit or had too much to lose to let her live. That probably could fit Jaulin, Zach or Karen for different reasons.
I still think the brother was copying some abuse he had witnessed, when he attacked that woman in the park. But who had he watched? The use of language suggested Jaulin was the most obvious candidate but now we've seen more of Karen and Zach it all seems fairly open again.
Did Sandrine want out of the setup and Zach or Karen killed her, even unintentionally, for letting them down? Had Jaulin realised that Sandrine was in touch with Zach and killed her out of jealousy, not wanting another man playing daddy to "his" boy? Was Jaulin actually working with the team as originally thought and forced Sandrine to play along?
Who actually benefited from Sandrine's death? She was helping Zach & co get places to live in and phones to use so was useful to them - no benefit in her death - so it must have been a pure rage attack instead if it was one of them.
Jaulin is the only one to benefit - as he potentially gets Leo if he plays his cards right and gets away with it.
Hmmmm 