Puerto Rico ? Angry pet owners and protesters demonstrated outside a town hall in a northern Puerto Rico city on Monday, as outrage grew over the killing of dozens of animals seized from residents of housing projects.

The crowd tried unsuccessfully to meet with Barceloneta Mayor Sol Luis Fontanez, who ordered last week’s seizure of the cats and dogs that were apparently later thrown from a 50-foot-high bridge.

Some protesters yelled “murderer.”

Fontanez, who pledged to resign if his government is found responsible, blamed a contractor hired to collect and euthanize the pets.

“My government acted according to the law,” he told The Associated Press.

With the help of television news broadcasts, a few animals rescued with broken bones and other injuries were reunited with their owners. Dozens more were buried in a mass grave.

On Monday, the contractor denied responsibility and accused residents of the housing projects of lying to get revenge for repeated raids to clear stray animals.