Chief Justice John G. Roberts Jr. of the U.S. Supreme Court referred the matter to Anthony J. Scirica, chief judge of the Philadelphia-based U.S. Court of Appeals for the Third Circuit.
Scirica named four judges to join him on the special committee conducting the inquiry: Third Circuit Judges Marjorie O. Rendell and Walter K. Stapleton, Chief Judge Harvey Bartle III of U.S. District Court in Philadelphia, and Chief Judge Garrett Brown Jr. of U.S. District Court in New Jersey.
The newspaper said that the images included a picture of two naked women on all fours painted to look like cows, and a video of a half-naked man cavorting with a sexually aroused farm animal.
The material is still circulating on the Internet, and that has led to a broad debate among lawyers and judges about the postings - and what to make of Kozinski.
"There's a wide spectrum of views," said University of Pittsburgh law professor Arthur D. Hellman, an expert on the federal judiciary and judicial ethics.
Kozinski at the time was presiding over an obscenity trial, and he stepped down from case and asked for the investigation. The judge told the Times that he thought the site was a private storage area, and that his son told him he might have placed some of the sexual content on the site.
Carl Tobias, a law professor at the University of Richmond who follows the Ninth Circuit, said the panel would have a number of issues to decide - what exactly the material was, whose it was, and whether it was available to the public or meant to be kept private.
Kozinski was the youngest judge ever appointed to a federal appeals court when he was named by President Ronald Reagan in 1985, at the age of 35, to the San Francisco-based Ninth Circuit, which is widely regarded as the most liberal federal appeals court in the nation.
Kozinski is known for his libertarian views and strong support for the First Amendment, and as a bit of an eccentric with a wide range of interests - bungee-jumping, snowboarding, raising chickens.
The panel will issue a report to the Third Circuit's judicial council, which will then determine whether Kozinski engaged in misconduct and whether he should be punished.
"There are a range of things that they could do, and most of them are like censure," Tobias said.
Hellman said he was struck by how quickly the investigation had started and how much had unfolded so far in public.
"This already has been done more out in the open than almost any other case," he said.
Center City lawyer Gregory Harvey said the choice of Scirica to lead such a sensitive investigation shows that he is well-regarded by Roberts.
"Having a hot potato, and concern that it go to someone who would deal with it appropriately, he immediately thought to send it to Tony Scirica," Harvey said.
Contact staff writer Emilie Lounsberry at 215-854-4828 or firstname.lastname@example.org.