CINCINNATI (CBSNewYork/AP) — Animal rights activists gathered Monday for a Memorial Day vigil for the gorilla killed at the Cincinnati Zoo after a 4-year-old boy slipped into an exhibit and a special zoo response team concluded his life was in danger.

Anthony Seta of Cincinnati called the 17-year-old western lowland gorilla’s death “a senseless tragedy,” but said the purpose Monday wasn’t to point fingers but a tribute to the gorilla named Harambe.

“People can shout at the parents and people can shout at the zoo,” Seta said. “The fact is that a gorilla that just celebrated his birthday has been killed.”

The gorilla’s birthday was May 27, the day before he was shot.

There has been an outpouring on social media of people upset about the killing of the member of an endangered species. A Facebook page called “Justice for Harambe” created Saturday night had drawn wide attention with more than 115,000 followers by Tuesday morning, along with online petitions and another page calling for a June 5 protest at the zoo.

Videos taken by zoo visitors showed the gorilla at times appeared to be protective of the boy, but also dragged him through the shallow moat.

The zoo’s director, Thane Maynard, said its dangerous animal response team that includes full-time animal keepers, veterinarians, and security staff made the right call to kill the gorilla. He said Saturday the 400-pound-plus gorilla didn’t appear to be attacking the child, but was in an “agitated situation” and was “extremely strong.” He said a tranquilizer wouldn’t have immediately felled the gorilla, leaving the child in danger.

“We are heartbroken about losing Harambe, but a child’s life was in danger and a quick decision had to be made,” Maynard said in statement Sunday.

The boy was taken to Cincinnati Children’s Hospital Medical Center for treatment and was released Saturday night. His parents said in a statement Sunday that he was “doing just fine.”

CBS2’s Andrea Grymes reported cellphone video showed the gorilla seemingly protecting the little boy until he grabs the little boy’s leg and drags him through the water.

Kim O’Connor, who shot the video, said she saw the boy and his mom before he climbed through the public barrier at the zoo.

“I heard the exchange while I’m waiting. ‘I’m going to go in.’ ‘No, you’re not.’ ‘I’m going to go in.’ ‘No, you’re not.’ The mother turns around to her other children,” O’Connor said.

Less than a minute later the boy made his way into the enclosure. O’Connor said the 400-pound gorilla ran out of the cave toward him.

A Facebook post from the boy’s mother said, “as a society we are quick to judge how a parent could take their eyes off of their child and if anyone knows me I keep a tight watch on my kids.”

Jack Hanna, director emeritus of the Columbus Zoo, said it was the right call to put the gorilla down.

“They cannot tranquilize it. It takes five to 10 minutes,” Hanna said. “We are all sorry. All of us in the zoo world are heartfelt for this thing, but thank goodness a human being is alive today because the decision the Cincinnati Zoo made.”

Many social media commenters have criticized the boy’s parents and said they should be held accountable. A Cincinnati police spokesman said there were no charges being considered. A spokeswoman for the family said Monday they had no plans to make additional comments.

“I do think there’s a degree of responsibility they have to be held to,” said Villanueva, a 28-year-old mother of two children. “You have to be watching your children at all times.”

The People for the Ethical Treatment of Animals released a statement from its primatologist Julia Gallucci saying the zoo should have had better barriers between humans and gorillas.

“This tragedy is exactly why PETA urges families to stay away from any facility that displays animals as sideshows for humans to gawk at,” the statement said.

The zoo said it’s the first such spectator breach at Gorilla World since it opened in 1978 and that the exhibit undergoes regular outside inspections. The zoo said earlier this year it plans to expand the exhibit.

Gorilla World remained closed Monday.

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