The head of the Senate Armed Services Committee wants to know why victims of the 2009 shooting at Fort Hood, Texas, still haven't received Purple Hearts.

In a letter to Defense Secretary Chuck Hagel on Thursday, Sen. John McCain, R-Ariz., said he was "disappointed" that the Army has not yet awarded the medals to victims of the attack, which killed 13 people and 32 wounded others.

As part of the fiscal 2015 Defense Authorization Act, Congress approved awarding Purple Hearts to troops "killed or wounded in domestic attacks inspired by foreign terrorist organizations." The language was aimed specifically at the Fort Hood victims, whose attack was classified as "workplace violence" and not battlefield injuries.

"As [legislation] was passed by Congress and signed into law by the President nearly a month ago, I am disappointed that the Army still has made no announcement for the award of the Purple Heart to the servicemembers killed or wounded [at] Fort Hood," McCain wrote. "Servicemembers and their families have been waiting more than five years for this award and further delay is inexcusable."

McCain said he wants the Defense Department to supply a timeline for awarding the medals by the end of January.

Republicans on Capitol Hill have been lobbying for the change in law and awarding of the medals since early 2010, as details emerged about the Army psychiatrist behind the attack. Army Maj. Nidal Hasan was inspired by al-Qaida teachings but faced murder charges rather than international terrorism charges. He was convicted and sentenced to death.

Army spokesman Wayne Hall said the service "is aware of the provision to modify the criteria for awarding Purple Hearts, and has begun a review to determine whether the Purple Heart could be awarded to the victims of the Fort Hood shooting — and other incidents — under the modified criteria."

No timetable has been set for that work.

Families of the Fort Hood victims have said they've faced thousands of dollars in uncovered medical expenses that would have been covered if the same injuries occurred in Iraq or Afghanistan.

They also have argued that the decision not to award the Purple Heart undermines the seriousness of the attack and the service of the injured troops.