Opening statements for the first civilian terrorism trial of a former Guantanamo Bay inmate began Tuesday in New York, minus a witness prosecutors called “critical” to their case, which has left experts divided over the terrorism trial of Ahmed Khalfan Ghailani.

Also, the trial into the investigation into the deaths of more than a dozen people at Fort Hood began Tuesday when witnesses provide testimony about last year's shooting spree by Army Maj. Nidal Malik Hassan, a 40-year-old Army psychiatrist.

Both trials are expected to be watched closely, both here and abroad.

As the first suspect held at the US military prison at Guantanamo Bay, Cuba to be tried in an American civilian court, Ghailani is accused of terrorism in the 1998 bombings of two US embassies in his native Tanzania and in Kenya, and conspiring with Al-Qaeda to kill Americans around the world. The attacks killed 224 people, including 12 US citizens.

Ghailani was captured in 2004 in Pakistan, he was sent to Guantanamo in 2006, and faces life in prison if convicted.

Hassan, meanwhile, was expected to appear at his hearing in a wheelchair, as he was left paralyzed by bullets during his shooting rampage on Nov. 5, 2009.

Hasan, 40, is charged with premeditated murder and attempted premeditated murder in the attack, which killed 13 people and wounded 32 others. It was the worst mass shooting at an American military base, and Hasan could face the death penalty.

Fort Hood is a major deployment point for the conflicts in Afghanistan and Iraq.

As the debate over how to prosecute Ghailani, Rep. Peter King, R-N.Y., told reporters that the recent judicial decision to not allow the testimony of a key government witness indicates problems that lie in store for the Justice Department if it attempts to use civilian courts to try other suspected terrorists, such as Khalid Sheikh Mohammed — the self-proclaimed mastermind behind 9/11.

The setback for US prosecutors came last week when Judge Lewis Kaplan of the US District Court in Manhattan ruled they could not use the testimony of the man who, the US government says, sold explosives to Ghailani.

Kaplan said the witness, Hussein Abebe, would not be allowed to testify because of the possibility that the government learned of his alleged role in the bombings through information it gathered from an interrogation it conducted of Ghailani in an overseas prison maintained by the CIA. The government has said Abebe was testifying voluntarily.

Ghailani’s lawyers applauded the judge’s ruling, saying he was tortured during his interrogation and the decision upheld American law.

Rep. King, the top-ranking House Republican on the Homeland Security committee said a federal judge’s ruling supports the GOP insistence that the White House was wrong to use civilian courts.

As for the pre-trial investigation of Hassan into the deaths at Fort Hood, survivors of the tragedy are expected to testify during the Article 32 investigation, a pre-trial investigation that could result in a general court martial, the most serious level of military trials that may end in the death penalty. The first session is scheduled to last until the end of the month, and a second session is set for Nov. 8 to Nov. 18. A third may be held in December.

Hassan’s lawyer, retired Col. John Galligan, would not tell reporters whether Hasan will plead insanity in his defense, and has advised his client against submitting to a mental health exam.

Hasan's motives are still unclear, but he was due for deployment before the shooting. As a psychiatrist at Walter Reed Medical Center, he had also sent messages to Anwar Al-Awlaki, a suspected terrorist and former imam at the mosque attended by two 9/11 hijackers, asking for spiritual guidance.

A practicing Muslim, Hasan was also said to have been unhappy about the treatment of Muslim service members.

The FBI has said Hasan came to its attention in December 2008 when a joint terrorism task force reviewed communication between Hasan and a person they were investigating. The agency said there were no indications at the time that Hasan had any accomplices or was part of a larger terror plot.

Early this year, the Pentagon adopted dozens of changes to policy and emergency procedures following an inquiry into the shooting found gaps in military rules on anti-terror and criminal threats.

The review found military policy on banned activities is unclear and does not allow commanders to act with guidance on potential threats to troop discipline and good order. It also found the Defense Department's commitment to the Joint Terrorism Task Force program with the FBI as “inadequate.”