Nearly four years after Maj. Nidal M. Hasan allegedly opened fire at the Fort Hood military base here, killing 13 people and wounding 32 others, the much-delayed court-martial of the Army psychiatrist is scheduled to begin Tuesday.

Hasan, a U.S.-born Muslim, is accused of carrying out one of the worst mass killings in U.S. history by firing more than 100 rounds during a seven-minute shooting spree at the Army base in central Texas on Nov. 5, 2009.

He has admitted to carrying out the attack but is prohibited by military law from entering a guilty plea because military prosecutors are pursuing the death sentence.

The 42-year-old, who is paralyzed from the waist down after being shot by Army civilian police, is representing himself and could cross-examine his alleged victims.

The trial, which was initially scheduled to begin more than 18 months ago, has been repeatedly delayed by legal issues. The judge first appointed to preside over the high-profile case was removed by the military’s highest court early last year after it ruled that he hadn’t appeared impartial.

Hasan also twice dismissed his legal team. He fought to represent himself and to keep his beard, which he says is an expression of his faith, in defiance of military regulations.

The psychologist had planned to argue that his actions were intended to save the lives of Taliban leaders in Afghanistan, but in June a judge ruled that he could not use a “defense of others” argument because there was no immediate threat from soldiers at the base.

Death sentences are rare in the military justice system and the case is taking place amid tight security, with Hasan flown in by helicopter from a local jail each day.

The military has not executed a service member since 1961, when a private was hanged at Fort Leavenworth in Kansas for raping an 11-year-old girl. In recent years, several death sentences have been commuted on appeal to life without parole, although five people remain on military death row, according to the Associated Press. As commander in chief, the president is required to sign off on a death sentence.

For Hasan to be convicted of murder, a 13-member panel of officers must decide unanimously that he is guilty. At a final pretrial hearing Monday, the judge, Col. Tara Osborn, indicated that the case is expected to last at least a month.

More than 130 victims of the shooting and their family members have joined a lawsuit seeking damages from the U.S. government, arguing that warnings that Hasan had become radicalized were repeatedly ignored because of “political correctness.”

The FBI’s Washington Field Office was aware that Hasan had exchanged e-mails with Anwar al-Awlaki, a radical U.S.-born Islamic cleric who was killed in a drone attack in Yemen in 2011, but did not inform the Defense Department. Hasan, who was soon to deploy to Afghanistan at the time of the attack, allegedly shouted “Allahu Akbar” — meaning “God is great” in Arabic — before opening fire.

The victims’ lawsuit is also seeking to have the shootings reclassified as a terrorist attack, rather than workplace violence, which would make victims eligible for benefits given to soldiers wounded or killed in combat.