With regard to Air marshalls - do you require one team per crew? All that is required is that the airline is known to have them, they do fly and this aircraft could have them on board. Something like a speed control camera box. Is there a camera inside?
Ai marshalls will not be the only solution. There must be greater security on the ground, personal IDs (everyone in the US is immediately identified by security no. why not something like this in Europe and the rest of the world), countries that do not boost security to be boycotted.
The time has come where governments must stop saying that they must fight by the rules. There are no rules. How many more innocents are going to die while the politicians pontificate? Force is understood by the terrorist (witness the kidnapping of a USSR citizen in Beirut in the 80s), words are seen to be a sign of weakness.