Military prosecutors had painted Fontana as a rogue and arrogant nurse who pumped patients full of fentanyl and morphine when they were not "dying quick enough." After the ruling, Fontana said he never second-guessed his treatment or dosages.
"My intention the whole time was to take care of dying patients," Fontana said.
Fontana, 36, said he wants to return to nursing.
Seeing the verdict as a validation, Fontana said he hoped the ruling would serve as a lesson for others tasked with making sure the terminally sick are comfortable. One doctor testified in the court-martial that he worried the case could chill the use of painkillers on the gravely ill.
Elizabeth Higginbotham, Fontana's attorney, said during closing arguments that a guilty verdict would open the "floodgates" for lawsuits against nurses when a dying patient finally goes.
"This could be a great educational tool nationwide," Fontana said. "You have to be observing the patients to the best of your ability."
Fontana worked at Lackland's Wilford Hall Medical Center, which is under the 59th Medical Wing. The hospital stood by the verdict by Col. William Burd, the military judge who rendered his decision about two hours after closing arguments.
Burd also acquitted Fontana on one count of conduct unbecoming an officer for altering medical records.
"We have great confidence in our military justice system and we believe a fair verdict was reached today," the 59th Medical Wing said in a statement.
The hospital said Fontana will now undergo a clinical competency evaluation to determine whether he can return to being an Air Force nurse. He continued working at Wilford Hall while awaiting trial, though was stationed in the library. away from patients.
During the weeklong trial, Air Force prosecutors accused Fontana of changing hospital records, trying to cover-up his tracks and chastising other nurses for not being "aggressive" enough in treating the end-of-life patients. Fontana knew the lethal effect of the dosages he was giving, prosecutors said.
"(Fontana said) because I'm liberal with patients and making them comfortable, they die within two or three hours, and that's the way it should be," prosecutor Capt. Brett Landry said during closing arguments.
The three who died were elderly, end-of-life patients. One of them, 83-year-old Silvestre Orosco, died a little more than three hours after being taken off life-sustaining machines and placed on "comfort care."
Prosecutors said Orosco died while Fontana covered for the patient's assigned nurse, who was on a lunch break. Fontana entered the room to hook up a new bag of the painkiller fentanyl, and Orosco died before his nurse returned from his break.
"Capt. Fontana euthanized Mr. Orosco because he wasn't dying quickly enough," Landry said.
Orosco died in June 2008; the two other patients both died Aug. 5 that year.
"We had so many patients die in the ICU that day. It was just coincidental," Fontana said. "It has nothing to do with the accusations."
In May, the presiding judge over a grand jury-type hearing recommended that prosecutors move forward with only one murder charge, but the military went ahead with all three.
Fontana has been in the Air Force since 2006 and served a tour in Iraq in 2007. He worked as an intensive care nurse at Wilford Hall, which primarily serves military personnel and retirees but provides emergency and trauma care to some civilians.