Victims of the Fort Hood shooting are pointing to news of a letter from the shooter, Nidal Hassan, as further evidence that the 2009 attack was a terrorism attack.

Hasan sent a two-page undated letter to Islamic State of Iraq and Syria leader Abu Bakr al-Baghdad asking to become a member of the extremist Islamic group, Fox News reported Friday after obtaining the letter.

In the letter, Hasan says it would be an honor to become an “obedient citizen soldier” for ISIS and signed the missive with his name and the abbreviation “SoA,” or “Soldier of Allah” – the same identification he used on business cards before the shooting.

News of the letter immediately stirred a renewed debate over why the administration designated the Fort Hood shootings an act of workplace violence rather than terrorism despite Hasan’s proven ties to al Qaeda.

A lawyer for the victims says Hasan’s letter to ISIS is just more “salt in their wounds.”

“It’s just yet another piece of evidence demonstrating that the government really has been lying about Hasan and his motivation for years,” Reed Rubinstein told the Washington Examiner Friday. “It’s almost like [Hasan is] taunting him – especially given the federal government’s response to the attacks.”

A coalition of 160 victims and family members of Hasan’s deadly rampage at Fort Hood have been fighting the Obama administration for nearly five years to label the shooting an act of terrorism.

The assault on the army post in Killeen, Texas, left 13 dead, more than 30 wounded by gunshots and dozens more injured. Survivors, many who suffered from multiple bullet wounds, have spent the past three years trying to rehabilitate their bodies and rebuild their lives.

For the service members who died and those who were wounded, the terrorism distinction would mean that the military considered that their injuries took place in a combat zone, making them eligible for Purple Heart medals and, the victims say, access to medical care and benefits similar to what soldiers wounded in Iraq or Afghanistan receive.

The victims point out that Hassan had several email exchanges with top al Qaeda leader Anwar al-Awlaki about the attack, about whether the attack was justified to “protect our brothers” and followed al-Awlaki’s advice to scream “Allah Akbar” (“God is Great”) to invoke fear before starting to shoot. Until his death by a drone airstrike in 2011, Yemen-based Awlaki was one of the United States’ top enemies.

Rep. Roger Williams, R-Texas, who represents part of Fort Hood, along with Rep. John Carter, R-Texas, said Hasan’s letter to ISIS is further evidence that the attack was “positively a terrorist attack carried out by an extremist as everyone already knows, including Hassan who has admitted as much.”

“Only the Obama administration denies this,” he said in an email to the Examiner Friday. “Again, I hope this administration will do the right thing for once by reclassifying this attack from workplace violence to what it really is — terrorism -- in order to get the victims and the families of those we lost the benefits they have earned and deserve."

A White House spokeswoman referred inquiries to the Pentagon, which did not respond to a request for comment.

Last August, a military jury sentenced Hasan to death by after just two hours of deliberation. He provided little defense, arguing that he acted to protect Islamic insurgents abroad from American aggressions and never denied being the gunman. He acknowledged pulling the trigger in a crowded waiting room where troops were getting final medical checks before deploying to Iraq and Afghanistan.

Williams is one of a handful of GOP members who have written letters to the Pentagon citing detailed evidence of al Qaeda involvement in the Fort Hood attack and asking Defense Secretaries Chuck Hagel and Leon Panetta before him for the terrorist designation.

The congressmen cited independent investigations by the Army, the Senate, and the Webster Commission, each showing that the Fort Hood attack was an act of terrorism. They also said military colleagues were well aware that Hasan was unstable but the military promoted him anyway without investigating complaints about his suspicious activity because they were afraid of being seen as biased against Muslims.

The 2014 defense authorization bill requires the Pentagon to provide Congress with a report of its review on whether some Fort Hood victims should receive Purple Hearts no later than 180 days after Obama signed the law.

Earlier this month Carter found out that the Pentagon had delayed the report for another year, in violation of the law.

Carter and Williams then sent a letter to Hagel arguing that Hagel lacks legal authority to disregard the deadline and demanding the report be submitted to Congress.

“Mr. Secretary, this is unacceptable,” they wrote. “…More than five years after the attack, we find it absurd that the Department of Defense needs yet another additional year to clarify if the victims are eligible for the Purple Heart.”

“Five years after this tragic event the Department of Defense has failed them,” they concluded.