Hanson died immediately from a broken neck, according to the coroner's autopsy report. Other injuries were sustained after her death, the report states.
Family members say they're relieved the young woman was killed instantly when the lion swiped or lunged at her at Cat Haven, a 100-acre private zoo run by the nonprofit group Project Survival.
"We're thankful to know she didn't suffer," Hanson's brother, Paul R. Hanson, told The Associated Press.
Family members said Friday they don't believe it was a mauling, but rather a lion's rough play that turned tragic.
"It sounds like it was an accident. Maybe the latch had not been completely closed. ... You know, house cats are smart, they can open doors," Paul Hanson said. "It wasn't a vicious attack ... because you would expect severe lacerations and biting on the neck and that was not the case."
Paul Hanson and his wife Tiffany Windle-Hanson, who was the victim's college roommate, believe the facility followed safety protocols.
"It was just a tragic accident," Windle-Hanson said.
Investigators were focusing on the cage door that the 5-year-old animal managed to escape through to reach the volunteer intern.
"The lion had been fed, the young woman was cleaning the large enclosure, and the lion was in the small cage," Hadden said. "The gate of the cage was partially open, which allowed the lion called Cous Cous to lift it up with his paw."
Hadden said the lion then ran at Hanson.
The coroner said Hanson was talking with a co-worker on a cellphone in the moments before she was killed. The co-worker became concerned when the conversation ended abruptly and Hanson failed to call back. The co-worker then called authorities when she went to check on Hanson.
Family members say Hanson was actually using a walkie-talkie, which they understood to be the policy at the animal park.
"She wasn't distracted, she wasn't like that," Windle-Hanson said. "It's a safety protocol to have walkie-talkies there, which is important in case a situation like this occurs."
Sheriff's deputies shot Cous Cous after the animal couldn't be coaxed away from Hanson's body.
Hanson had been working for two months as an intern at Cat Haven.
Her father, Paul Hanson, described his daughter as a "fearless" lover of big cats and said her goal was to work with the animals at an accredited zoo. She died doing what she loves, he said.
Hanson's Facebook page is plastered with photos of her petting tigers and other big cats. She told her father she was frustrated that Cat Haven did not allow direct contact with animals.
"Dianna had a tremendous respect for big cats. It's something she wanted to do since she was 3 years old," said Dianna Hanson's aunt, Karen Postema, who lives in Laurel, Mont.
"She was a vivacious, terrific kid, and we are heartbroken about her death," she said. "But we wanted people to know that she loved what she was doing, and we don't want this accident to cast dispersions on her character or hurt the program at Cat Haven."
Dale Anderson, the owner of the zoo, said safety protocols were in place but he would not discuss them because they are a part of the law enforcement investigation.
Anderson said he's the only person allowed in the enclosure when lions are present.
"We want to assure the community that we have followed all safety protocols," Anderson said. "We have been incident-free since 1998."
He said the facility will reopen to the public Sunday.
When the attack occurred, Anderson said he and two other Cat Haven workers had left to take a cheetah to exhibit at a school. Hanson and another worker remained at the facility.
Whether Hanson was performing a function that placed her in danger is being investigated by Cal-OSHA, which also is trying to determine if employees were properly instructed about potential danger, as required.
In addition, the U.S. Department of Agriculture, which enforces the federal Animal Welfare Act, is also looking to understand why the lion turned on the intern.
USDA inspectors conduct multiple unannounced inspections of Cat Haven every year and never had found a violation, Sacks said. Federal regulations pertain only to animal treatment.
Cat Haven breeds and keeps lions, tigers, jaguars, lynx and other exotic cats and takes them out for public appearances. There are 29 wild cats left at the park, including one female lion that lived with Cous Cous in the same enclosure.
On Friday, Hanson's family announced that a fund has been set up in her memory and urged people to donate to the wildlife organizations she loved, including Cat Haven.