DALLAS (MCT) — If history is any judge, the Army will find it difficult to impose the death penalty on the accused killer in the bloodiest mass shooting on a U.S. military base in history.

Military experts say Army Maj. Nidal Malik Hasan is almost certain to face capital charges before an Army court-martial. But they warn that death penalty cases are so rare in the military, and so prone to big mistakes, that death sentences rarely stick.

And executions themselves are almost nonexistent. The last American serviceman to be executed was hanged in 1961.

Since 1984, when Congress revamped military law regarding the death penalty, the United States has sought to execute 49 service members, though never an officer. Fifteen of those defendants were convicted and sentenced to death.

But in 10 cases, the sentences later were commuted by their commanders — or overturned on appeal.

That leaves five condemned soldiers, Marines or sailors sitting on death row at Fort Leavenworth, Kan.

Of those, only a single soldier has exhausted his military appeals and been ordered to die by the president, as required. And his case has been held up by a last-minute habeas corpus appeal in a civilian U.S. District Court in Kansas, even though the military has done all it can to send him to the federal death chamber in Terre Haute, Ind.

"Death penalty cases are so rare that almost everyone who tries a death military case is new," said Dwight Sullivan, a Marine Corps Reserve colonel and civilian appellate attorney for the Air Force. He has succeeded in having death sentences for three condemned servicemen overturned or commuted.

"Almost everyone involved — from the commander to the judge to the jurors to the defense attorneys — is doing it for the first time," Sullivan said.

The investigation into what happened Thursday has only just begun, and military officials have said they have not ruled out the possibility that Hasan had help from civilians in planning his attack.

Experts said it's far more likely that the military will prosecute its own, but the U.S. attorney's office could bring capital charges in federal court as part of a broader conspiracy prosecution. Eight times, service members sentenced to die have seen their cases or convictions overturned by appellate courts, as judges — both military and civilian — have found fault with the handling of their trials.

The mistakes have included inadequate defense counsel, tainted juries and bad decisions by military judges — a litany of blunders that offers a cautionary tale for commanders at Fort Hood, who probably will face significant pressure to move quickly in meting out justice in the slaughter.