I must confess that during my last night flight, I certainly didn't sleep, but I was wearing a noise-cancelling headphone (with music playing loud inside) while staring at my laptop playing, err, writing important business reports. The pax next to me could have been robbed without me noticing anything, let alone a bag at the other end of the cabin.

If the cabin was nearly near empty, and the robbery appeared in the front Affaires cabin, I guess the 5 victims (or 4 victims and perpetrator faking to be victims) could be all the persons in said cabin, also, making it easy for taking all the purses in one go. 5 out of 5 sleeping is more credible than 20 or 25 : theft could be from a J pax (of the rear cabin) going to the toilets. I am somehow unconvinced that people who fly in J would risk doing that (because they couldn't be sure they would collect that much money) purely because everyone is asleep, though.