Harambe was shot dead after a four-year-old boy fell into the zoo's enclosure
More than 250,000 people have signed a petition calling for police to investigate the parents of a child who fell into a zoo's gorilla enclosure, prompting keepers to shoot the animal.
Outrage has mounted over the Cincinnati Zoo's killing of Harambe, a Western lowland gorilla, whose species is listed as endangered.
Harambe was shot dead after dragging the four-year-old boy through shallow water and up a rock wall.
The petition called "Justice For Harambe" demands a police investigation into the family's "negligence".
It reads: "We the undersigned believe that the child would not have been able to enter the enclosure under proper parental supervision.
"Witnesses claim that they heard the child state that he wished to go into the enclosure and was actively trying to breach the barriers. This should have prompted the parents to immediately remove the child from the vicinity.
"It is believed that the situation was caused by parental negligence and the zoo is not responsible for the child's injuries and possible trauma.
"We the undersigned want the parents to be held accountable for the lack of supervision and negligence that caused Harambe to lose his life."
Dozens of animal rights activists held a vigil at the zoo on Monday and flowers were laid at a gorilla statue.
Anthony Seta, one of the activists, said the death was "a senseless tragedy" but denied that those at the vigil were trying to lay the blame at anyone's door.
"People can shout at the parents and people can shout at the zoo," he said. "The fact is that a gorilla that just celebrated his birthday has been killed."
Michelle Gregg, the boy's mother, has asked others not to judge her because "accidents happen".
She said her son was recovering from a concussion and a few scrapes.
A family statement on Sunday expressed condolences to the zoo for the loss of the 17-year-old gorilla.
"We are so thankful to the Lord that our child is safe. He is home and doing just fine," the statement said.
"We extend our heartfelt thanks for the quick action by the Cincinnati Zoo staff. We know that this was a very difficult decision for them, and that they are grieving the loss of their gorilla."
The zoo's dangerous animal response team shot Harambe dead about 10 minutes after he encountered the child.
Tranquillisers were not an option because they could have a delayed effect and agitated the gorilla further, zoo officials said.
Thayne Maynard, the zoo's director, said on Monday: "Looking back, we would make the same decision. The gorilla was clearly agitated. The gorilla was clearly disoriented."