AP

Dogs are shown behind bars in a composite photograph after they were caught near where where a woman, her baby and a teenage couple were found dead and covered in dog bites. The attacks set off a debate about the city's love-hate relationship with its canine population, and the guilt or innocence of 25 dogs trapped near the scene of the nightmarish killings.

MEXICO CITY -- Police scoured a hilly urban park for feral dogs and tested dozens of captured animals on Tuesday in a hunt for those responsible for four fatal maulings that have set off a fierce debate about how to handle the thousands of stray dogs that roam this massive city.

Authorities have captured 25 dogs near the scene of the attacks in the capital's poor Iztapalapa district, but rather than calm residents, photos of the forlorn dogs brought a wave of sympathy for the animals, doubts about their involvement in the killings and debate about government handling of the stray-dog problem.

Activists started an online campaign protesting the dogs' innocence and calling for authorities not to euthanize them. Tens of thousands of dogs are euthanized each year in Mexico if they are captured by animal control officers and not claimed within 72 hours. Many people re-posted the images of the dogs staring sadly from behind bars at an animal shelter.

The hashtag for the campaign became the top trending topic on Twitter in Mexico by midday Tuesday, with some users furiously accusing the authorities of cruelty to animals and others sarcastically calling the dogs "political prisoners" and mocking the fuss over the fate of the animals.

With more than 20 million people living in greater Mexico City, many of them lacking the resources to properly care for pets, stay dogs are an established problem. Nonprofit organizations such as Compassion Without Borders and Mexico City Dogs appeal for donations to help address the situation, and a 2007 documentary, "Companions to None," focused on abandoned pets.

Officials said they were testing the captured dogs' fur for blood and examining their stomach contents to determine if they were the killers of the four people whose bodies were found covered in dog bites in two separate incidents in recent days.

Grim discoveries
Neighbors of the Cerro de la Estrella park found the bodies of a 26-year-old woman and a 1-year-old child in the area on Dec. 29, authorities 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 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 at around 7 p.m. pleading for help, Milenio Television reported.

Mexico City prosecutors said that due to the gravity of the wounds they believed at least 10 dogs were involved in each attack.

Dozens of officers returned to the park Tuesday to capture more of the feral dogs, which live in caves and hollows in the area.

"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. Residents of their neighborhood started running frantically to collect their dogs when police began seizing strays Monday night, she said.

Official response
The furor has forced a public response from Mexico City 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 their health," he told reporters after a midday press conference.

He also said the government would launch a new program to spay and neuter dogs, sending 25 mobile surgical units to neighborhoods where residents would be encouraged to take advantage of free sterilization for their pets.

Eduardo Verdugo / AP

Police fan out as they search for stray dogs in a park on the hilltop borough of Iztapalapa in southeast Mexico City on Tuesday.