Mexicans protest detention of dogs in killings, tests come back negative

A puppy that was caught near the site of four fatal maulings sits inside a cage at a city dog pound in Mexico City,Wednesday, Jan. 9, 2013. Authorities have captured dozens of 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. (AP Photo/Dario Lopez-Mills) (The Associated Press)

One of the dogs that was caught near the site of four fatal maulings sits inside a cage at a city dog pound in Mexico City, Wednesday, Jan. 9, 2013. Authorities have captured dozens of 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. (AP Photo/Dario Lopez-Mills) (The Associated Press)

A litter of puppies that was caught near the site of four fatal maulings sit inside a cage at a city dog pound in Mexico City,Wednesday, Jan. 9, 2013. Authorities have captured dozens of 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. (AP Photo/Dario Lopez-Mills) (The Associated Press)