Emergency service recordings have revealed the confusion and panic after a three-year-old boy plunged into Cincinnati Zoo's gorilla exhibit and was picked up by one of the animals.
During the 911 recordings of Saturday's incident, which ended when the 17-year-old western lowland gorilla called Harambe was shot dead by zoo staff, the boy's mother is heard pleading for help while repeatedly shouting at her son: "Be calm!"
The mother, who is not identified, tells the dispatcher: "He's dragging my son! I can't watch this!", after the child dropped about 15 feet into the zoo's Gorilla World exhibit.
Minutes later, the zoo's dangerous animal response team killed the gorilla to protect the boy.
Since then, there have been numerous questions about how the boy got past the barriers around the exhibit.
Police are investigating the actions of the child's parents and US government inspectors are planning their own review of the zoo.
The boy's family did not comment on the police investigation, but released a statement saying he continued to do well.
They also thanked the zoo for protecting his life.
His mother said in the 911 call that her son had fallen into the exhibit and a gorilla was standing over him.
The dispatcher told her that responders were on their way, and the caller yelled four times: "Be calm!"
A record of police calls shows nine minutes passed between the first emergency call about the boy falling into the enclosure and when the child was safe.
The zoo has an open viewing area that was among the first of its kind and is now common in many zoos around the country.
The zoo says it will look at whether it needs to reinforce the barriers even though it considers the enclosure more secure than what is required.
The breach, zoo director Thane Maynard said, was the first time a visitor had entered its Gorilla World exhibit, which opened in 1978.
A federal inspection less than two months ago found no problems with the exhibit.
On Wednesday, the boy's family said he "is still doing well", they continued to "praise God" and were also thankful to the zoo "for their actions taken to protect our child".
While they have been blamed for the gorilla's death by some on social media, the family expressed appreciation for those offering support.
The statement said some people had offered money, which they say they will not accept.
"If anyone wishes to make a gift, we recommend a donation to the Cincinnati Zoo in Harambe's name," said the statement released through publicist Gail Myers.
Police said their investigation would look at the parents' actions, not the operation of the zoo, which is overseen by the US Department of Agriculture.
Police will then discuss with prosecutors whether charges should be filed.
At least two animal rights groups were holding the zoo responsible for the death of the gorilla, claiming that the barrier made up of a fence, bushes and a moat was inadequate.