Shit happens.
That news sounds like a gag. A bad gag actually.
Seriously, this is quite disturbing. Add to that the several nights spent by a journalist roaming in the sensitive areas of the Heathrow airport. It is clear that the security of the airports is too weak. It's insane that the borders between the different areas and the luggages are not better checked. I thought all the luggages were viewed with Xrays to detect suspect objects and materials.
It'd be so easy to set the registration 1 or 2 hours before the lift off, and pass the luggages through Xrays in front of the passangers and require them to open them if there is a doubt exist about an object. It'd require a lot of personnel but that's the price of safety.
Regarding the unknown passenger with ~150grams of PE in his/her luggages, the customs of the destination airports are informed of that " momentary lack of surveillance ", so he/she shouldn't have too much trouble with the local authorities. I guess/hope the French Police stamped the packet with a "Property of the French Government" or "French Police" or a blue,white,red label. And if I were him I'd go dispose the packet either at the airport police office or to the nearest police office.