Although American and European intelligence agencies have, since the 1990s, established close cooperation when it comes to counter-terrorism, there are still national differences that produce friction. For example European privacy laws are different make illegal, or very difficult, data gathering (like credit card or phone records) that is easy for the police and intel organizations in the United States. This is another lingering aftereffect of World War II, when Nazi secret police did whatever they wanted and left many bad memories. But when the Europeans saw how powerful some of these search tools were, they made exceptions for counter-terrorism work. Despite that there are continue to be problems because of the many remaining differences between American and European policing.
European intelligence officials understand the usefulness of the American approach more than their elected superiors but have to follow orders. Sometimes the Americans will do the searches and quietly pass their findings on to the Europeans. While all members of the EU (European Union) share some common laws and customs, the legal systems and police procedures in each EU member nation are different and this can often complicate terrorism investigations. Some terrorists know how to take advantage of these differences but since the Islamic terrorist groups recruit mainly from the shallow end of the gene pool, a lot of European Islamic terrorists have a hard time understanding and using the various legal tricks to avoid detection or prosecution.