A Jordanian military court on Monday slapped a soldier, who had killed three American trainers previous year, with a life sentence.
The defendant had pleaded "not guilty", saying he opened fire because he feared the base was coming under attack.
The parents of one of the slain US soldiers and the father and sister of another sat quietly as the judge announced his ruling to a crowded courtroom.
Jordanian authorities initially said the trainers had been killed after they failed to stop.
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The representatives of the U.S. Embassy observed the trial and judicial proceedings, which confirmed that the deceased U.S. service members followed all established procedures when accessing the base the day of the incident, as we have noted before.
"We are reassured to see the perpetrator brought to justice", it said.
In the attack, for which no extremist motive has been proven, he killed Staff Sgt. Matthew C. Lewellen, a 27-year-old from Missouri; Staff Sgt. Kevin J. McEnroe, a 30-year-old from Arizona; and Staff Sgt. James F. Moriarty, a 27-year-old from Texas.
Jordan, a staunch USA ally, hosts several hundred US contractors in a military cooperation programme which includes the stationing of U.S. F-16 fighter jets. His lawyer said the defense respects the court's decision, but that the verdict will be appealed.