While initial reports indicated police shot and killed Martinez, 31, Hauge said the fatal bullet came from the man's own gun.
"Ballistics show he was struck by two different bullets," Hauge said. "One that struck him in the knee or lower leg, disabling him, came from [a deputy's] weapon. There was another bullet that struck the center chest, through his heart. That bullet was recovered, and it matches the bullets fired from his own gun."
The prosecutor said that weapon was also used to kill Valdivia.
"She was shot twice, and both shots were fired by Mr. Martinez at relatively close range," Hauge said.
Two deputies were wounded during the shootout before a third opened fire, hitting Martinez, officials said.
Valdivia was last seen in Utah on the night of Jan. 18 at a South Salt Lake foster-care facility. The Utah Division of Child and Family Services placed the girl there after she ran away from home last year. Later, police found her with Martinez in California on Oct. 15, 2010.
A spokesman for the Valdivia family has said Astrid and Martinez "were lovers," though police have said they never found evidence of sexual abuse. Martinez's family, meanwhile, has said Astrid was troubled by her family situation and looked to Martinez for help. Martinez had been a friend of the Valdivia family.
"I don't know what to think," said Martinez's sister, Crissty Werner, on Thursday. "It just hurts. We're told two different things. … The reports, in the beginning, were that the [deputy] shot him, and months later, the story is changing. It's just odd. It's just weird."
Werner said her family hopes to review investigators' reports on their own for "closure" in the matter.
"Who knows if there is a cover-up?" she said. "If they think, 'He's dead. He can't defend himself. It doesn't matter anyway.' … How do they know that she didn't want to live without him and she tried to kill herself?"
Messages left with a spokesman for Astrid Valdivia's family weren't immediately returned.
Hauge said it could take another month to complete his report.
Prosecutors are still waiting for reports from different medical examiners' offices. Surveillance cameras captured "significant portions" of the shootout, he said.