“We can’t change what happened in the past,” said US attorney Stephen Muldrow. “Animals died.”

However, he stressed that going to court would only delay the transfer of the zoo’s remaining animals, which number some 300 from a tarantula to a lone elephant.

“The welfare of the animals is a top priority,” Muldrow said at a news conference.

He added that the violations at the zoo spanned “many years” with “various administrations failing to ensure animal welfare.”

He said it was an institutional problem as well as a lack of resources: “There was no intentional harm to the animals.”

But activists say ending the federal investigations means impunity reigned and no justice will be served for the animals that died or fell ill.

“We demanded that the federal government do its job: investigate violations,” said Christian Ríos, an attorney and chair of an animal rights committee at the Association of Lawyers of Puerto Rico. “This leaves a bad taste in our mouths.”

In the past decade, a government-appointed commission found two cougars dying and raised concerns about an underweight chimpanzee, a rhinoceros named Felipe who walked with a limp and a lack of shelter for animals including a kangaroo and a porcupine.

In January, an American black bear named Nina, who had stopped eating, died of a heart attack at the age of more than 20. Black bears can live up to 35 years in captivity.

Meanwhile, officials last week had to euthanize a cougar who had been diagnosed with cancer, Muldrow said.

He said almost all the animals will be transferred within the next six months, noting that two eagles have already been removed because the zoo did not have a license to care for them, and that two owls and two anacondas have also been transferred elsewhere on the island .

Earlier this month, Pat Craig, executive director of The Wildlife Animal Sanctuary in Colorado and Texas, told The Associated Press that the organization would take in up to 50% of the zoo’s animals.

However, it is still unknown where certain animals, including the lone elephant named “Mundi”, would end up. Muldrow said officials are trying to find an elephant sanctuary because they are a social species and should be kept in groups.

The zoo, which opened in 1954, has remained closed since Hurricanes Irma and Maria ravaged Puerto Rico in September 2017.