I may have missed it, but can anyone confirm that the gas cylinder was taken aboard as CARRY-ON luggage?
Or, if it was checked in, then there is no way the security guards can find it!
At the end of the day, the passenger IS responsible for what THEY pack. There is a little box that says "I AGREE" which must be ticked when you purchase your online ticket.
IF it was taken aboard as Carry-on, then I agree that "security" must shoulder some of the blame.