DUNLAP, California (Reuters) - The California wildlife sanctuary where an African lion attacked and killed a worker last week reopened on Sunday, allowing the public to view all the remaining wild cats, including the lion's mate.

Project Survival's Cat Haven resumed regular operations, including guided tours, with the consent of the family of Dianna Hanson, founder Dale Anderson said at a news conference.

Hanson, a 24-year-old intern who had been working at the park since January, was attacked while cleaning an empty cat enclosure.

A 4-year-old male lion named Cous Cous escaped from his feeding pen, apparently by pushing open an improperly secured gate, and pounced on Hanson, fracturing her neck and killing her instantly, Fresno County Coroner David Hadden said.

Sheriff's deputies shot and killed the lion, which weighed at least 400 pounds (181 kgs), after they failed to coax him away from Hanson's body.

Cat Haven officials at the news conference on Sunday read a letter from Donna Anderson, Hanson's mother, who said she was "living every mother's worst nightmare in losing a cherished child."

"I am pleased that Cat Haven is re-opening today and share in their sorrow in the loss of Cous Cous," the letter said. "It is my desire that they continue their mission in support of saving my daughter's beloved creatures."

The sanctuary had been closed to the public since Wednesday's attack.

State and local agencies are investigating whether Cat Haven violated any safety procedures that could have safeguarded against such an attack.

"What we're finding out so far leads us to believe that the door was accidentally left open," said Fresno County Sheriff Margaret Mims, who also spoke at the news conference.

"Unfortunately, we have no witnesses," Mims added. "Some answers we may not ever know."

Hanson had been speaking on a walkie-talkie to the head keeper of Cat Haven, when their communication abruptly ended, Mims said. The keeper went to check on her but did not think it was an emergency and it took her about 45 minutes to reach Hanson, Mims said.

Cous Cous and his mate, Pele, were Barbary lions, a species from the region between Morocco and Egypt. The species is extinct in the wild. Cous Cous had been handled by humans since he was weeks old.

Pele was among the cats on display on Sunday.

Danielle Jones, 43, was among the visitors to Cat Haven on Sunday. She runs a sanctuary for disabled and elderly animals nearby.

"Being an animal lover and advocate, I feel real bad for Dianna's family and my heart goes out to Cous Cous," Jones said.

Cat Haven, a 100-acre (16-hectare) sanctuary in Dunlap, California, run by the group Project Survival and located about 40 miles east of Fresno, is still home to 29 tigers, leopards and other wild cats.

Hanson earned a biology degree in 2011 from Western Washington University. Last year she spent six months in Kenya working on a wild feline reserve.

The Hanson family has set up a fund in Dianna's honor that will benefit her favorite charitable organizations, including Cat Haven.