In a case that outraged animal-rights activists and generated national attention, a trial began Monday for a Chester County man charged with killing his neighbor's dogs because he believed they posed a threat to his sheep.

Gabriel Pilotti, 73, of Chester Springs, was charged with cruelty to animals for shooting the two Bernese mountain dogs - 2-year-old Angus and 1-year-old Fiona - after they had escaped the fenced yard of their owners, Mary and William Bock.

As a result of the attention drawn to the case, Pilotti has been the target of threats.

In his opening statement, Kevin Pierce, assistant district attorney, said Pilotti willfully and maliciously killed the dogs in cold blood and then left a voice message for a neighbor, bragging about the incident.

Pierce said the dogs were not attacking the sheep or baring their teeth. Argus was shot in the head as he trotted toward Pilotti, and Fiona was shot as she ran away. Pilotti did not try to yell at the dogs or chase them away with a broom, Pierce said.

"He chose to go to the most extreme measure first," Pierce said.

Defense attorney Thomas Ramsay acknowledged that Pilotti killed the dogs but said that his client thought he was within the law.

"The man took actions he willfully thought he could take," Ramsay said. His client's actions were influenced by a May 2012 incident in which other dogs entered Pilotti's neighbors' property and killed their livestock, Ramsay said. Pilotti then killed those loose dogs.

"He is a shepherd to his sheep," Ramsay said. "They are his whole life."

The Bock family has since adopted three other Bernese mountain dogs for their five children, ages 5 to 12.