"I had to help. I knew I had to help," he told reporters in Phoenix on Tuesday. "To me there was no choice."
It happened very quickly as Yoxall drove west along Interstate 10 just west of the small town of Tonopah. Yoxall saw the emergency lights of a state patrol SUV and flares on the ground. He spied a man on top of trooper Ed Andersson, a 27-year veteran, and got out with his gun.
Yoxall said he told the attacker to stop. The assailant didn't and Yoxall killed him.
"This is something that I will live with, but I wouldn't change it, because another man got to go home to his family and his family gets to keep him a little while longer and that's the important part," Yoxall said of the January 12 predawn incident.
After the shooting he needed time to cope with taking a man's life, Yoxall said, so he told the media no interviews.
"I did save somebody's life that morning, but I had to take somebody else's life in the process and that's difficult to reconcile," said Yoxall, whose voice shook and whose eyes welled with tears through much of the news conference.
He has talked with other people who have gone through similar experiences, he said, and has sought the counsel of his pastor.
Yoxal, 43, said he believes as a gun owner he has a duty to practice proper shooting techniques and does so several times each year. He declined to say what kind of weapon he used, though authorities have described it as a 9mm pistol.
He has no military or law enforcement training but said he trains at a range in the desert with friends who do.
Yoxall said he has an innate motivation to help others.
When he saw Leonard Penuelas-Escobar "savagely beating" Andersson, he felt he had to defend the trooper. On Tuesday, he refused the "hero" label.
"I'm an ordinary person. I go to work, I do photography, I hang out with my friends and family, I read," the maintenance manager said. "I was put in extraordinary circumstances and I may have acted heroically, but I don't consider myself a hero at all."
The director of the Arizona Department of Public Safety thinks otherwise.
"I'm proud to introduce him and (proud of) what he has done for this agency," Col. Frank Milstead said at a news conference.
Milstead later said Andersson is still recovering from a bullet that entered his right shoulder. The trooper lost part of the humerus in his right arm and will need more surgeries.
He is in good spirits, Milstead said.
When asked whether the trooper has met the man who saved him, Milstead was unsure but said if it hasn't happened it will. A department spokesman, Quentin Mehr, said the two have yet to meet.
Police still do not know why Penuelas, 37, shot Andersson, who was stopping to investigate a rollover crash that killed a woman in Penuelas' vehicle. The woman, Vanessa Monique Lopez-Ruiz, 23, died from her injuries at a hospital.
Milstead said last week that when Andersson approached Penuelas, he was seated and cradling Lopez. As the trooper got close, Penuelas shot him with a 9mm pistol.
Penuelas then attacked the trooper, Milstead said, and Yoxall pulled up while on his way to California with his fiancee.
Yoxall shot Penuelas twice and, thinking the assailant was down for good, he went to the trooper to give first aid.
Suddenly Penuelas got up and came at them. Yoxall shot him in the head, Milstead said.
There is no dashcam or body camera video from the incident.
Another man stopped at the scene and used the trooper's portable radio to call for help, though emergency responders were already on the way, responding to Andersson's call for medical help for Lopez.
Penuelas was in the country illegally, Milstead said, adding that he thought the native of Mexico may have once been a member of the federal police.