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The arrests seemed like a startling wakeup call to America: Federal authorities said a group of would-be terrorists were foiled in a plot to sneak onto a New Jersey military base and kill soldiers.

The federal government argues that the May 2007 arrests of Serdar Tatar, Mohamad Ibrahim Shnewer and the brothers Dritan, Eljvir and Shain Duka saved innocent lives. Defense lawyers contend there was no plot and that the government paid an informant to get them to discuss one.

The trial, which opens with jury selection Monday, isn't a whodunit. The key question will center on whether the men would have done it.

The case will be watched closely because it represents a type of pre-emptive prosecution that has grown more common in U.S. terrorism cases since the Sept. 11, 2001, attacks — which troubles some experts.

"Lately, the government has been instructing its informants and taking a more active approach in planning and participation" of illegal acts, said Henry Klingeman, a former federal prosecutor who was the defense lawyer in another New Jersey terrorism case three years ago.

The trial will test the government's strategy in terrorism prosecutions, said Robert Chesney, a Wake Forest University law professor who studies domestic terrorism law.

Unlike many terrorism cases, the Fort Dix case doesn't involve the transfer of money to people who intended to do harm. It's about people accused of planning to take lives themselves. "It's a very important case," Chesney said.

The five suspects in the alleged Fort Dix plot all face charges of attempted murder and conspiracy to murder uniformed military personnel; four of them are also charged with weapons offenses. All have been in federal custody since they were arrested and face life in prison if they're convicted.

It could take three weeks or more just to seat a jury of 12 from the 1,500 citizens who have been called. Testimony could last for months.

The government's investigation into the alleged plot began with a tip from Brian Morgenstern, a clerk at a Circuit City electronics store in Mount Laurel.

He called police in January 2006 after he was troubled by a video that customers asked him to convert to a DVD. Authorities say the home-shot footage featured men at a firing range shouting "Allah Akbar," Arabic for "God is Great."

The government then paid Mahmoud Omar, an Egyptian national on probation in a bank fraud case, to infiltrate the group.

The 39-year-old Omar recorded hundreds of hours of conversations with the younger men, all foreign-born Muslims in their 20s who had lived for several years in the southern New Jersey suburbs of Philadelphia.

The government alleges the plotters were homegrown — a cab driver, three roofing workers and a convenience store clerk who had applied for jobs as a police officer — and that they did not have any connections to outside terror groups. But prosecutors say they were influenced by other terrorist acts, cheering and laughing at gruesome propaganda videos that show Americans being killed.

Federal prosecutors plan to try to show that Dritan Duka tried to buy an AK-47 in Camden as early as 2005, and that Shnewer suggested other targets, including the White House, FBI and CIA headquarters, the U.S. Capitol and Philadelphia International Airport.

They also will allege that Tatar helped plan the attack using a map of Fort Dix he took from his father's pizza shop, which is just outside the New Jersey Army installation used mostly to train reservists for duty in Afghanistan and Iraq.

Prosecutors also will try to establish that the men took two trips to Pennsylvania's Pocono Mountains for training missions that included shooting at firing ranges with automatic weapons.

Agron Abdullahu, a supermarket baker who was on the trips, pleaded guilty last year to providing weapons to some of the others, who are illegal immigrants. Abdullahu, who is now serving a 20-month prison sentence, is not expected to testify at the trial. He has denied any knowledge of a plot.

Prosecutors will also likely detail how Omar brokered a deal for the men to buy (from federal agents) a small arsenal of three AK-47s, two M-16s and four handguns.

Defense lawyers have portrayed Omar as the mastermind of any plot that existed and show that most of their clients were oblivious to any plan.

Michael Riley, who is representing Shain Duka, said the defense will probably play more, and longer, snippets of recorded conversations than prosecutors will. The defense will try to show that while their clients may have liked to shoot guns and held anti-American views, they were not moving ahead with a plan to kill.

"Our guys are saying, 'What are you talking about?"' when an attack is mentioned, Riley said.

Shnewer's lawyer, Rocco Cipparone, has said he will consider using an entrapment defense, trying to persuade jurors that if there was a plot, his client was led into it by Omar.

Legal experts say the government has expanded the use of conspiracy laws in terrorism cases since the Sept. 11 terrorist attacks.

John Parry, a law professor at Oregon's Lewis and Clark University, said the government sometimes charges people with being in a conspiracy to carry out terrorism even if they did not take steps to carry it out.

"I'm skeptical, personally, that we're in such a serious emergency that we should be pushing the envelope of conspiracy laws," Parry said.