More than 45 months have passed since 13 people were shot to death, and 32 more wounded, during a shooting spree at the Fort Hood military base in Killeen, Texas.

Yet the court-martial of the admitted killer, Maj. Nidal Malik, didn’t begin until five days ago at the fort.

The defendant, representing himself, told the military court as the trial opened Tuesday that “the evidence will clearly show that I am the shooter.”

So there’s apparently no question about his guilt.

However, other troubling questions persist. Among them:

Why did it take so long to bring Maj. Hasan to trial?

Why was he allowed to stay in the Army for so long despite numerous tirades that plainly identified his dangerous, radical Islamic world view — and the harrowing security hazard he presented?

Why has the Pentagon insisted on classifying, as “workplace violence,” this terrorist act by an Islamist zealot who, according to witnesses, shouted “Allahu akbar” (“God is great”) while shooting dozens of innocent people at a Soldier Readiness Processing Center?

Before that carnage, Maj. Hasan, a Virginia-born Army psychiatrist, had defended Osama bin Laden during a lecture at the Walter Reed National Military Medical Center in Washington. He also had publicly, repeatedly and vehemently defended Islamic radical suicide bombers.

Some — but not all — of his superiors had stated the obvious by warning, in writing, that he was “a ticking time bomb.”

The FBI determined that Maj. Hasan had frequently communicated via emails with terrorist Anwar al-Awlaki, a high-ranking al-Qaida propagandist killed by a U.S. drone attack in Yemen in 2011. But the FBI didn’t act on that information.

According to Maj. Hasan himself, however, he did act on his bitter resentment of U.S. foreign policy by opening fire in a crowded room on Nov. 5, 2009, at Fort Hood.

Yet according to the Defense Department, this remains a case of “work-related” violence. The Pentagon, in 2010 training material, even likened the Fort Hood massacre to acts of mayhem by unhinged postal workers.

That absurd designation deprives the wounded victims, and the dead victims’ loved ones, of benefits they would have rightly received if this mass murder had been accurately deemed a terrorist act.

On Friday, attorneys assigned to assist Maj. Hasan in his defense were granted leave from the trial to prepare their appeal to be relieved of that duty. They argued that they don’t want to participate in his “repugnant” effort to draw the death penalty.

Meanwhile, though Maj. Hasan can’t plead guilty under military-court regulations because of that capital-punishment possibility, he can — and has — used the trial to further vent his vile views.

And you don’t need a law degree to reach a negative verdict about this galling case of justice delayed.