I am now reconsidering Mark.
He knew that there was going to be the warehouse bust.
He knew that Leon was going to meet Baptise and when and where.
However, Baptise knew all those things too.
However, I don't think Mark knew that they were meeting Ziane in prison, but Baptiste did.
I can't work out though why Baptiste would want to abduct a child and/or cover it up and also be very good at investigating it.
Mark on the other hand could be being blackmailed by the gang- we'll take your son (although this went wrong and the got Ollie?), look what happened to Ollie, you have to do what we want you too to keep James safe?