The fatal mauling of four people by feral dogs in a Mexico City park set off debate Tuesday about the city's love/hate relationship with its dog population, and the guilt or innocence of 25 animals trapped near the scene of the nightmarish killings.

Mexico City's mayor said the government would launch a new program to spay and neuter the hundreds of thousands of dogs who wander the city, sending 25 mobile surgical units to neighborhoods where residents would be encouraged to take advantage of free sterilization for their pets. Animal advocates called for Mexico City residents to rethink a pet-owning culture that often treats dogs as disposable, saying the police failed to enforce a ban on sales of puppies and kittens in the streets.

Police photos of the forlorn, skinny strays captured in the wooded, hilltop park where a woman, her baby and a teenage couple were killed in two separate incidents set off an online campaign protesting their innocence and calling for authorities not to euthanize them. Many people re-posted the images of the dogs, a collection of small- to medium-size strays of various types, staring sadly from behind bars at an animal shelter in the lower-income borough of Iztapalapa in southeast Mexico City.

The hashtag for the campaign became the top trending topic on Twitter in Mexico by midday Tuesday, forcing a public response from Mayor Miguel Angel Mancera, who called for animal-rights groups to help study the guilt or innocence of the 25 dogs, and the broader effort to reduce the number of street dogs in Mexico City.

"We're not taking any decision. The dogs are in a shelter and we have to check on the health," he told reporters after a midday press conference.

Antemio Maya, president of the Street Dog Protection association, said there are no reliable figures for the number of street dogs in Mexico City, and many of the animals are pets released to wander the streets during the day, then return home when their owners come back from work. He said many people in Mexico City treat dogs as disposable, buying one for their children for Christmas, then abandoning it in a park or suburb when the responsibility become overwhelming.

He said estimates for the overall number of dogs in the city of nearly 9 million people range from 1.2 million to 3 million animals.

Neighbors of the Cerro de la Estrella, a partly wooded hilltop park surrounded by Iztapalapa, found the bodies of a 26-year-old woman and a 1-year-old child in the area on Dec. 29, authorities in Mexico's capital said.

The woman, Shunashi Mendoza, was missing her left arm, and prosecutors said that both she and the boy had bled to death.

Then on Saturday visitors to the same park found the bodies of Alejandra Ruiz, 15, and her boyfriend Samuel Martinez, 16, who had gone to the park Saturday afternoon and were found dead from blood loss.

The girl called her sister Diana Ruiz at around 7 p.m. pleading for help.

Ruiz told Milenio Television she thought her sister was joking and still doesn't believe her sister was killed by dogs despite the call.

Mexico City prosecutors said that autopsies determined that all of the victims had died of dog bites, and that due to the gravity of the wounds they believed at least 10 dogs were involved in each attack.

Dozens of officers from the city's Animal Protection Brigade searched the park for feral dogs again on Tuesday.

"Officer, you're hunting for dogs again, but don't you already supposedly have the 25 killers in custody?" shouted Liliana Hernandez, a psychologist and self-described street dog rights activist who lives near the park.

Hernandez said many people let their dogs out during the day because their cinderblock homes are too small to keep them inside. Resident of their neighborhood started running frantically to collect their dogs when police began seizing strays Monday night, she said.

A veterinarian at the Iztapalapa shelter said it appeared that at least one of the captured dogs had been a pet.

"A family came and recognized a dog but we couldn't give him to them because investigators have to decide what to do," he said on condition of anonymity because he was not authorized to speak to the press.