The thing is, that American hegemony on the old continent is history since the end of the cold war. From the 350.000 GIs in Germany there are maybe between 60.000 and 25.000 left with a shrinking development. The city-police of Frankfurt has probably more operative man-power than the US in Europe. The current US influence in western Europe is that low that some governments like Germany or France do not even support the recent US wars by lip-service anymore. During the cold war we Germans were bound as a occupied country to support you at least with billions and bazillions of Dollars. Today the US do not even get some benevolent words on their way if we Europeans are not convinced of your actions.
Some things might have changed but we are for sure no enemies of you because of that. We try to help in your WOT where we can but we do it by our rules. There are many common interests and nations like the UK, Germany, France, Italy, Denmark, Spain etc. etc. etc. even support your wars in Afghanistan or in Iraq with soldiers, men and material. Beside of this we still share values, religion and offspring.
That does not change the fact that it is up to us to deal with terrorists on our own territory and not up to the US or anyone else. Therefore people who highjack our citizens on our territory are criminals and therefore bound to go to jail if we get them. No matter if they have a contract of your government or not.
A example: The El-Masri hijack.
In some cases the identities of the involved CIA agents are known and they are already wanted over a international warrant of arrest by EURO- and INTERPOL. Therefore they are well advised never ever put again a foot on European soil. In Europe we strictly seperate between judiciary (the judges) and executive (the government). Nobody (not even Merkel, Sarko or Prodi) will be able to help your agents if they ever should be caught.