In situations of military conflict, civil strife, lawlessness, bad governance, and human rights violations, terrorists find it easier to hide, train and prepare their attacks.
In the fight against terrorism, national agencies keep full control over their police forces, security and intelligence agencies and judicial authorities.
Look at Iraq; look at Afghanistan, where at great personal physical risk people have gone to the polls and have rejected the appeal from Bin Laden and his allies to stay at home.
Police forces collect information to be used in a public court to get people convicted. Security services gather information that does not necessarily lead to people being prosecuted and in many cases needs to remain confidential.