​El Salvador's widespread violence reached an unexpected corner with the brutal and fatal beating of the national zoo's beloved hippopotamus Gustavito.

Even among a population numbed by a staggering human death toll due to gang violence in recent years, the animal's death late Sunday stirred outrage.

They kill us like flies, but this tops it all. — Street vendor Martin Castillo

Salvadorans mourned through social media and some left flowers at the gate of the zoo, which has been closed until further notice.

"Here we're used to seeing the dead every day," Martin Castillo, a street vendor in the capital's historic downtown, said Monday. "They kill us like flies, but this tops it all. They killed an animal that only entertained us."

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.

Investigation opened

The attack occurred sometime Tuesday night a week ago. But zookeepers did not discover the hippo's injuries until Thursday because he did not leave his pool. Gustavito died late Sunday.

Justice Minister Mauricio Ramirez Landaverde said an investigation had been opened.

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.

"We're angry," said Carmen Rogel, who often brings her grandson to the zoo. "We didn't know they had killed Gustavito and were surprised when we arrived and the gate was closed."