Ultimately, I suppose it comes down to perspective. As somebody noted above, European law is a work in progress and conflicts between national and supranational jurisdiction are frequent enough that those of us living in Europe see nothing surprising in them.

Conversely, the multiple levels of lawlessness of the contemplated assassination stands out all the more when viewed from within the context of Europe's legal scrupulousness.

I'm not a lawyer, but it seems to me that the situation embodies at least the following aspects, all of which I find worth consideration:

• Extrajudicial execution = violation of due process and the rule of law - a fundamental universal (for the purposes of this discussion) principle.
  
• Assassination of an individual on the territory of a sovereign nation: assassination of the citizens of another country is a casus belli with historical precedent (think WWI); the present situation might very well be conceivably construed as an act of war.
  
• Delegation of war-making powers to a private contractor: a can of worms in and of itself.

The fact is that what we're experiencing right now is a top-down disaster. -Paul Krugman