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Wiretaps obtained under a Patriot Act provision aimed at gathering foreign intelligence wrongly helped convict Muslim immigrants in a domestic criminal case, defense lawyers argued Monday in U.S. appeals court in Philadelphia.

The lawyers represent five young men convicted of plotting a deadly strike at a New Jersey military base. Prosecutors call evidence in the three-month trial overwhelming and the two wiretaps in question incidental to the conviction.

Defense lawyer Michael E. Riley argued otherwise.

"We don't know which of the nails in the coffin were the final nails in the coffin (for jurors)," he said.

A federal jury in Camden, N.J., convicted the men — Mohamad Shnewer, Serdar Tatar, and brothers Dritan, Eljvir and Shain Duka — in December 2008 of conspiring to kill U.S. military personnel at Fort Dix. All but Tatar are serving life terms.

Prosecutors charged that the Philadelphia-area residents, inspired by al-Qaida, had taken training trips to the Pocono Mountains and scouted out Fort Dix, an Army base in New Jersey used primarily to train reservists for duty in Iraq, and other sites.

"The issue the jury had to decide was, where they serious? Did they mean to attack soldiers, or were they just talking to blow off steam?" Assistant U.S. Attorney Norman Gross said Monday, summarizing the crux of the complex case.

Prosecutors concede the group did not necessarily have a specific plan to attack Fort Dix and were probably months away from an attack. The jury acquitted the men of attempted murder charges.

The three-judge appeals panel had agreed to hear arguments about the constitutionality of the wiretaps under the Foreign Intelligence Surveillance Act, as it was amended by the Patriot Act.

Justice Department lawyers argue that other U.S. courts have upheld the searches, which are authorized not by a federal magistrate, but by a specially-created FISA court. High-level Justice Department officials must first certify the need for the wiretaps for national-security purposes.

"In order to effectively conduct counterespionage, you need the kind of protections FISA has (established)," Gross argued. "You simply can't have the same kind of disclosures."

The yearlong investigation began in 2007 after a clerk at a Circuit City store told police that some customers had asked him to transfer onto DVD some video footage of them firing assault weapons and screaming about jihad.

The defense also argued on appeal that the FBI used dubious informants to entrap the young men and that their taped discussions amounted to little more than a religious debate about jihad, or holy war.

U.S. appellate judges hearing the case debated whether U.S. District Judge Robert Kugler was right to let prosecutors play beheading videotapes to the jury. The tapes did not relate to any of the defendants.

A defense lawyer argued that jurors turned against his clients after seeing the tapes, although the actual beheadings were not shown in court.

Appeals Court Judge Marjorie Rendell said the violent tapes may show the defendants' state of mind, since they watched them obsessively. But her colleague, Judge Theodore McKee, disagreed.

"It's an example of blatantly overtrying the case. That said, I'm not saying it's reversible (error)," McKee said.

The judges did not indicate when they would rule.

Four of the defendants had attended public high school in Cherry Hill, N.J. The men include Shnewer, a Jordanian-born cab driver; Tatar, a Turkish-born convenience store clerk; and the Dukas, ethnic Albanians from the former Yugoslavia, who had a roofing business

A few dozen members of the local Muslim community, including the Dukas' parents, filled one section of the courtroom.

All three brothers are being held in a maximum-security prison in Colorado, their mother said.

"They are together, but they can't see each other," Cuzurada Duka, 52, told The Associated Press.

She insists her sons were egged on by the FBI informants who visited the family home. She has only been able to visit them once in Colorado.

"They were OK, because they are strong. They know they are innocent. They know one day the truth will come out," she said.