The U.S. Army soldier who is accused of committing one of the worst mass shootings in American history against his fellow, unarmed soldiers will begin his military trial Tuesday after a series of delays.

Maj. Nidal Malik Hasan doesn’t deny that he carried out the November 2009 attack at Fort Hood, Texas, which left 13 people dead and more than 30 others wounded. There are dozens of witnesses who saw it happen. Military law prohibits him from entering a guilty plea because authorities are seeking the death penalty. But if he is convicted and sentenced to death in a trial that starts Tuesday, there are likely years, if not decades, of appeals ahead, and experts say he may never make it to the death chamber at all.

While the Hasan case is unusually complex, experts also say the military justice system is unaccustomed to dealing with death penalty cases and has struggled to avoid overturned sentences.

Eleven of the 16 death sentences handed down by military juries in the last 30 years have been overturned, according to an academic study and court records. No active-duty soldier has been executed since 1961.

A reversed verdict or sentence on appeal in the Hasan case would be a fiasco for prosecutors and the Army. That’s one reason why prosecutors and the military judge have been deliberate leading up to trial, said Geoffrey Corn, a professor at the South Texas College of Law and former military lawyer.

“The public looks and says, `This is an obviously guilty defendant. What’s so hard about this?”‘ Corn said. “What seems so simple is, in fact, relatively complicated.”

Hasan is charged with 13 specifications of premeditated murder and 32 specifications of attempted premeditated murder. Thirteen officers from around the country who hold Hasan’s rank or higher will serve on the jury for a trial that will likely last one month and probably longer. They must be unanimous to convict Hasan of murder and sentence him to death. Three-quarters of the panel must vote for an attempted murder conviction.

The jury will likely hear from victims and relatives of the dead. A handful of victims still carry bullet fragments in their body. Others have nightmares.

“It never goes away — being upset that it’s taken so long for this trial to come,” said Staff Sgt. Alonzo Lunsford, who was shot in the head, stomach and upper body. “So now’s the day of reckoning, which is positive — very positive.”

The trial’s start has been delayed over and over, often due to requests from Hasan. Any of the hundreds of decisions large or small could be fair game on appeal. The entire record will be scrutinized by military appeals courts that have overturned most of the death sentences they’ve considered.

“A good prosecutor, in military parlance, would be foolish to fight only the close battle,” Corn said. “He’s got to fight the close battle and the future battle. And the future battle is the appellate record.”

Hasan has twice dismissed his lawyers and now plans to represent himself at trial. He’s suggested he wants to argue the killings were in “defense of others” — namely, members of the Taliban fighting Americans in Afghanistan. The trial judge, Col. Tara Osborn, has so far denied that strategy.

Hasan has grown a beard while in custody that he says expresses his Muslim faith, but violates military rules on decorum. After a military judge ordered him forcibly shaved, an appeals court stayed that order and took another judge off the case.

The last man executed in the military system was Pvt. John Bennett, hanged in 1961 for raping an 11-year-old girl. Five men are on the military death row at Fort Leavenworth, Kan., but none are close to being executed.

An inmate was taken off death row just last year. Kenneth Parker was condemned for killing two fellow Marines in North Carolina, including Lance Cpl. Rodney Page. But Parker was given life without parole last September by an appeals court. The court found his trial judge should have not allowed him to be tried for both murders at the same time, nor should the judge have allowed testimony that the appeals court said was irrelevant to the crimes.

Parker’s accomplice in the killings, Wade Walker, was also sentenced to death, only for the sentence to be overturned.

Examples abound of other death sentences set aside. They include William Kreutzer Jr., who killed one soldier and wounded 18 others in a 1995 shooting spree at Fort Bragg, N.C.; James T. Murphy, who killed his wife in Germany by smashing her head with a hammer; and Melvin Turner, who killed his 11-month-old daughter with a razor blade.

Part of the problem, experts say, is that death penalty cases are rare in military courts.

A study in the Journal of Criminal Law & Criminology identified just 41 cases between 1984 and 2005 where a defendant faced a court-martial on a capital charge. Meanwhile, more than 500 people have been executed since 1982 in the civilian system in Texas, the nation’s most active death-penalty state.

While lawyers and judges in Texas may get multiple death penalty cases a year, many military judges and lawyers often are on their first, said Victor Hansen, another former prosecutor who now teaches at the New England School of Law. The military courts that are required to review each death-penalty verdict are also more cautious and likely to pinpoint possible errors that might pass muster at a civilian court, Hansen and Corn said.

Hansen compared the military’s conundrum to small states that have a death-penalty law on the books, but never use it.

“You don’t have a lot of experience or institutional knowledge,” said Hansen, who compared it to “the reinventing of the wheel every time one is done.”

If Hasan is convicted and sentenced to death, his case will automatically go before appeals courts for the Army and the armed forces. If those courts affirm the sentence, he could ask the Supreme Court for a review or file motions in federal civilian courts.

The president, as the military commander in chief, must sign off on a death sentence.

“If history is any guide, it’s going to be a long, long, long time,” Hansen said.

The so-called “chatter” about a terror plot that led the Obama administration to close 22 U.S. embassies and consulates Sunday across the Muslim world goes beyond anything heard before the Sept. 11 terrorist attacks, according to the top Republican on the Senate Intelligence Committee and Fox News sources.

Sen. Saxby Chambliss, of Georgia, said Sunday the so-called “chatter” detected by U.S. intelligence agencies that led the Obama administration to order the closures and issue a global travel warning to Americans is “very reminiscent of what we saw pre-9/11.”

Sources told Fox News the chatter picked up by U.S. intelligence agents over the past two weeks exceeds anything in the last decade. And it included Al Qaeda leader Ayman al-Zawahiri demanding that key leaders of the terror network in the Arabian Peninsula step up their activities in the wake of recent killings of top terrorists.

The information is the most recent and detailed since the administration made the announcement Thursday.

Officials have not said whether the closures will extend beyond Sunday. However, Maria Harf, a State Department spokeswoman, said following the announcement that the U.S. outposts might be closed “additional days,” depending on additional analysis. Other Western countries have also closed outposts in the region.

A Mideast diplomat says al-Zawahiri “pressuring” Al Qaeda in the Arabian Peninsula to launch new terrorist attacks on Western and American targets is “unprecedented.”

Sources also told Fox News the extraordinary volume of “chatter” follows months of “absolute quietness” on terrorist phone lines, computer outlets, websites and other communication outlets.

They said al-Zawahiri has always been a bigger proponent than his predecessor, Usama bin Laden, of a more centrally managed Al Qaeda terrorist structure, has always sought to “micromanage” AQAP, and is attempting now to assert management authority over individual cells, even if it is largely illusory.

The sources said the closures and the travel alert were also prompted by a spate of recent Al Qaeda-led prison breaks, including one in Aleppo, Syria, this weekend that have freed hundreds of Al Qaeda operatives over the last month.

The return of these individuals to their respective “battlefields” may have contributed to the escalation in “chatter” and has heightened American alarm over the plotting. Recent prison breaks have been orchestrated at Abu Ghraib in Afghanistan, as well as sites in Iraq, Libya and Pakistan.

Yemen is said to be cooperating closely with U.S. intelligence in this period, and the data given to the CIA is said to have informed the embassy closures.

Mideast diplomats say National Security Adviser Susan Rice is a driving force in the closures. They say that Rice is still stinging from the criticism about her role in the fatal attacks on the United State’s outpost in Libya and determined to avoid a repeat.

Chambliss told NBC’s “Meet the Press” it is “the most serious threat I’ve seen in a number of years.”

On Saturday, top U.S. officials met to review the threat, according to the White House.

Even as the White House labels Benghazi a “phony scandal,” a raft of new allegations and concerns is once again bringing the controversy back to the forefront in Washington.

Fox News has learned that at least five CIA employees were forced to sign additional nondisclosure agreements this past spring in the wake of the Benghazi attack. These employees had already signed such agreements before the attack but were made to sign new agreements aimed at discouraging survivors from leaking their stories to the media or anyone else.

CNN has also reported that dozens of people working for the CIA were in Benghazi on the night of the attack, and that employees are being intimidated into staying silent.

CIA spokesman Dean Boyd pushed back on the claims in a written statement released Friday.

“CIA employees are always free to speak to Congress if they want to and there is an established process to facilitate such communication on a confidential basis. The CIA enabled all officers involved in Benghazi the opportunity to meet with Congress,” he said. “We are not aware of any CIA employee who has experienced retaliation, including any non-routine  security procedures, or who has been prevented from sharing a concern with Congress about the Benghazi incident.”

But the claims have fueled concerns by lawmakers that, while the government is spending much energy on keeping Benghazi personnel quiet, not enough progress has been made in tracking down those actually responsible for the strike.

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Lawmakers pointed to a report by CNN earlier this week in which Ansar al-Sharia leader Ahmed Abu Khattala told the network that nobody from the American government has contacted him. Ansar al-Sharia is a militant group in the region considered of high interest in connection with the attack.

“Even the investigative team did not try to contact me,” he told CNN.

Lawmakers penned a letter earlier this week to newly confirmed FBI Director James Comey urging him to aggressively identify and pursue the suspects.

“It has been more than 10 months since the attacks. We appear to be no closer to knowing who was responsible today than we were in the early weeks following the attack,” they wrote. “This is simply unacceptable.”

Some in Congress continue to press for a select committee to investigate the Sept. 11 attacks. Rep. Steve Stockman, R-Texas, announced on Thursday that he plans to try and force a vote in Congress on creating such an investigative panel. House rules could make this an uphill effort for Stockman.

Separately, House Oversight and Government Reform Committee Chairman Darrell Issa, R-Calif., on Thursday issued two new subpoenas to the State Department for documents on Benghazi.

The White House earlier this week claimed it considers the controversy over Benghazi — specifically over how officials initially described the nature of the attack — as “phony.”

But the details about the lengths to which the government is going to keep people quiet has raised additional questions.

The CNN report said some CIA operatives are being forced to take “frequent, even monthly” lie detector tests. They’re reportedly trying to root out who is talking to reporters or members of Congress.

“You have no idea the amount of pressure being brought to bear on anyone with knowledge of this operation,” one source was quoted as saying.

The nature of that operation is unclear to this day. One source told CNN that 21 Americans had been working at the CIA annex in Benghazi at the time of the attack. Initially, the compound was merely described as a diplomatic consulate.

Egyptian security officials said Thursday that they have arrested the Muslim Brotherhood’s leader, after the military ousted Brotherhood-aligned President Mohammed Morsi and replaced him with the supreme justice of the Constitutional Court.

The officials said Mohammed Badie was arrested Wednesday night in a resort village in Marsa Matrouh, a Mediterranean coastal city west of Cairo not far from the Libyan border. He had been staying in a villa owned by a businessman with Brotherhood links.

The officials spoke Thursday on condition of anonymity because they were not authorized to speak to the press.

He was flown to Cairo on a military helicopter, according to the officials, who spoke on condition of anonymity because they were not authorized to speak to the media.

The prosecutor’s office, a day after the overthrow, ordered Badie’s arrest, and his deputy Khairat el-Shater, sources told Reuters. The two were reportedly wanted for inciting the killing of protesters in front of the Brotherhood’s headquarters in Cairo’s southern neighborhood called Mokattam, the AFP reported.

Al Ahram, a major state newspaper, reported that eight protesters were killed while attacking the headquarters, The New York Times reported.

Publicly, the Brotherhood urged members to avoid violence during the most recent upheaval.

In addition to the two high-ranking leaders, Al-Ahram reported that arrest warrants were issued for 300 other members of the Brotherhood, Reuters reported.

Badie and el-Shater were widely believed by the opposition to be the real power in Egypt during Morsi’s tenure. As of Wednesday night, Badie was last known to be holed up at a tourist resort on the Mediterranean coast near the Libyan border, with security forces surrounding the building.

The leader of the Brotherhood’s political arm — Freedom and Justice Party — and another of Badie’s deputies have been detained.

The arrests and warrants against Brotherhood leaders signal a crackdown by the military against Islamists who have dominated the political scene in Egypt since the ouster in 2011 of autocrat Hosni Mubarak.

Embattled Syrian President Bashar al-Assad told a state-run newspaper that Morsi’s fall means the end of “political Islam.”

The Brotherhood’s television station, Misr 25, has been taken off the air along with several TV networks run by Islamists. Morsi’s critics have long accused the stations of sowing divisions among Egyptians and inciting against secularists, liberals, Christians and Shiite Muslims with their hard-line rhetoric.

Adi Mansour, Egypt’s interim leader, made overtures to the Brotherhood in his inauguration.

“The Muslim Brotherhood are part of this people and are invited to participate in building the nation as nobody will be excluded, and if they respond to the invitation, they will be welcomed,” he said, according to Reuters.

Still, Morsi’s ouster is seen by many as a blow to the Brotherhood’s push for influence in North Africa just two years after the fall of Mubarak. The Wall Street Journal reports that the change of tides may push some Islamists to take a pass on democracy and turn to violence.

The Brotherhood has hemorrhaged support. Under Brotherhood rule, crime has spiked, the economy has tanked and the country’s politics have grown dangerously polarized, the Journal’s report said. The popular swell of discontent with the Brotherhood and the movement’s governing shortcomings has been acknowledged even by the movement’s most defiant leaders.

“This is the first time in the history of the Brotherhood that it is the people and not the regime that are acting against the movement,” said Ibrahim al-Hudaibi, a prominent former member of the group, told the paper.

Morsi was ousted in what was described by the presidential palace as a “complete military coup.” The White House has not labeled Morsi ouster a coup. Doing so would have U.S. aid implications.

Ahmed Aref, a spokesman for the Muslim Brotherhood party, told Reuters both Morsi and an aide were being held but he didn’t know their location. A security official said they were at a military intelligence facility, Reuters reported.

Morsi said on his presidential Facebook page that the military’s action “presents a military coup and it is unacceptable.”

At least 14 people were killed in clashes between Morsi’s supporters and opponents following the announcement, Reuters said, citing the state news agency MENA. Egyptian troops, including commandos in full combat gear, were deployed across much of Cairo, including at key facilities, on bridges over the Nile River and at major intersections

Eight of the dead were reported to be in the northern city of Marsa Matrouh, with three killed and at least 50 wounded in Alexandria. Another three were killed in the southern city of Minya.

A U.S. official said nonessential diplomats and embassy families had been ordered to leave Egypt amid the unrest. The State Department issued a warning urging U.S. citizens in the country to leave.