Police are currently searching for those responsible for entering Gustavito’s enclosure and beating him with blunt and sharp objects, CNN reported.
Zoo officials noticed on Thursday that Gustavito was acting strangely and would not come out of the water in his enclosure or eat.
Zoo director Vladan Henriquez said at a news conference that the hippo was covered with bruises and puncture wounds after apparently being attacked with metal bars, knives and rocks.
Henriquez said at a news conference that Gustavito sustained injuries to his feet and cheek while he was likely trying to defend himself. He said the wounds might have been from an ice pick.
"There were injuries inside his mouth," Henríquez said.
Despite the zoo’s best efforts, the 15-year-old hippo died on Sunday. Authorities are currently investigating the incident, BBC reported.
Officials have described it as a cowardly and inhumane attack on one of the most iconic animals at the city's zoo.
On social media, many used the hashtag #Gustavito to mourn the hippo’s passing and call for justice.
"Here we're used to seeing the dead every day," Martin Castillo, a street vendor in the capital's historic downtown, said.
"They kill us like flies, but this tops it all. They killed an animal that only entertained us."
El Salvador is one of the world's most violent countries, recording 5,278 homicides last year, or an average of 14 people killed per day. Most of the killings have been blamed on powerful street gangs.
Gustavito was born and raised in Guatemala, but was brought to El Salvador 13 years ago.
(USA Today - Feb 28, 2017)