Former Attorney General John Ashcroft cannot be sued by an American Muslim arrested after 9/11, the U.S. Supreme Court ruled Tuesday.

In a 5-3 vote, the court found that Ashcroft did not violate the constitutional rights of Abdullah al-Kidd in 2003 when he was arrested and held without charges for 16 days.

The law under which al-Kidd was detained was intended to make sure witnesses testify in criminal proceedings, the court decided.

"Qualified immunity gives government officials breathing room to make reasonable, but mistaken judgments about open legal questions," Justice Antonin Scalia wrote for the majority.

In a federal lawsuit, the Kansas-born al-Kidd claimed his detention was a violation the Fourth Amendment, which bars unreasonable search and seizure.

"[Al-Kidd's] ordeal is a grim reminder of the need to install safeguards against disrespect for human dignity, constraints that will control officialdom even in perilous times," Justice Ruth Bader Ginsburg said in opposition.

Tuesday's decision reverses an appeals court ruling saying Ashcroft could be liable for his role in the arrest.