Cumbria tiger attack: Sarah McClay dies of her injuries
The death of a zoo worker attacked by a tiger could have been due to "human or technical factors", police said.
Sarah McClay, 24, was attacked by a Sumatran tiger in an enclosure at South Lakes Wild Animal Park, near Dalton-in-Furness, Cumbria, on Friday.
Detectives are investigating how Ms McClay and the animal came into contact, "with tragic consequences".
Park owner David Gill said there was "no reason" for Ms McClay to be in the enclosure with the tigers.
Det Supt Andrew Slattery from Cumbria Police said its inquiry was centred on "the management of dangerous animals".
Mr Slattery said "systems and protocols" at the park were being investigated.
"At this stage it is not a criminal investigation," he said.
Police said compartments in the tiger enclosure were connected by lockable doors but systems in place to ensure staff and animals were kept apart had "failed".
Mr Gill said Ms McClay, who is originally from Glasgow, was a "very experienced" staff member who had worked with big cats and was "proficient and passionate" at her job, but staff should have no direct contact with the tigers.
"We have very strict protocols and procedures for working with big cats, but it seems she failed to follow correct procedures," he said.
"For inexplicable reasons she opened a door and walked into the enclosure.
"We will never know why she entered without telling anyone. There was no reason for her to go in there."
Mr Gill described Ms McClay as a "bubbly, happy girl" and described her death as a "tragedy for her family and all the staff".
He said the attack happened at about 16:00 BST on Friday and he believed it was witnessed by one member of the public.
The park was closed early and all visitors evacuated from the area, but following discussions with investigators and staff a decision had been made to reopen as usual on Saturday.
Mr Gill said: "The public were not at risk and we followed all our accident procedures to the letter.
"We had a meeting of all staff at 5.30pm and asked what they wanted. There was a huge consensus of opinion that we carry on.
"It would not do any good to close the park as there is no safety issue."
He said the Sumatran tiger, which has lived at the park for 10 years since it was a cub, would not be destroyed.
"He didn't do anything wrong. He's a tiger and his natural instinct is to kill. We all know that and that's why all the protocols are in place.
"He didn't make a mistake, he was just there. We don't blame him for what happened."
The attack is being investigated by Cumbria Police and Barrow Borough Council.
Ms McClay's family were "very shocked and distressed", officers said.