Ashcroft v. Al-Kidd
To show that Ashcroft could be sued, al-Kidd's lawyers had to meet a very high burden of proof.  They needed to prove that Ashcroft was directly involved in holding al-Kidd, or that he knew what was happening to al-Kidd.  The Court ruled that al-Kidd's lawyers had not proved these things.  They suggested that al-Kidd's detention was handled mostly by people who were much less powerful than Ashcroft.