BOISE - The former attorneys for convicted murderer Joseph Duncan are asking a judge to let them testify in secret about whether Duncan was mentally competent during his death penalty hearing four years ago.

Duncan's current attorneys - not the lawyers who represented him in 2008 - filed a motion Sunday in Boise's U.S. District Court asking a judge to either close the courtroom for the former attorneys to testify or to allow them to testify at another private location.

Such secrecy is needed, the attorneys say, to keep from scaring other clients, who may fear that their lawyers will someday reveal protected information about them in court.

"The solution for this problem is for the court to allow defense witnesses who are subject to the attorney-client privilege to testify outside the presence of the public," Duncan's attorneys wrote in their motion to the court.

Duncan snatched 9-year-old Dylan Groene and Dylan's younger sister from their Wolf Lodge home after murdering several of their family members in 2005. He kept the children at a remote Montana campsite for weeks before he shot Dylan and returned with Dylan's sister to Coeur d'Alene, where he was arrested.

He was convicted in state court of murdering the children's family members and sentenced to life in prison without parole. His crimes against the two children were handled in federal court, where Duncan pleaded guilty, represented himself, and was sentenced to death.

In 2011, however, the 9th U.S. Circuit Court of Appeals ruled that the federal judge should have held a hearing to determine if Duncan was competent when he waived his right to appeal his sentence. Last week U.S. District Judge Edward Lodge began presiding over a retrospective competency hearing, designed to help him decide if Duncan was competent back in 2008.

Duncan's defense team first raised the possibility that his former attorneys may try to testify in secret last week - a proposal that federal prosecutors said caught them by surprise.

At the time, U.S. Attorney Wendy Olson told the judge that federal policy bars her from agreeing to a closed courtroom without getting prior approval from leaders with the U.S. Department of Justice, a process that can take weeks.

Olson has until later this week to file a response to Duncan's motion.