<sigh> since you put it that way! lol. Now it's even more confusing!
Ok, it could be Cambronne, for the v good reasons above. He would have influence no doubt with the authorities.
Robbie's Mom. Not sure, it's the money & influence thing that's the catch here. Outsider at best. But agree she may have helped Neil.
We also don't know if the people who helped Neil, if he did have help, are one & the same as the ones pushing the French Police. Could be totally separate! <sigh>
As for the photos, mmm, could be Marcel in them, looks more similar to Robbie than Max. <throws yet another spanner in> Why would Marcel do it, money. Cambronne may be paying him!
Or the photos were genuine & Robbie did kill Neil. They did get upto some kinky stuff, so breath control wouldn't surprise me.
My head hurts from all the different scenarios, so will leave the guesswork for now.
More than likely it's none of the above! lol.