The deputies were conducting a house-to-house search in Norwalk after receiving a call about an armed man at a park.
The deputies asked a resident of a home, Eddie Perez, to secure his pit bull so that they could search the property. Officials said the pit bull overpowered Perez and ran into the street and attacked the sheriff's dog.
"The pit bull bit the K-9's throat and pinned it on its back in the street," the Sheriff's Department said in a statement. "Due to the aggressive and violent nature of the pit bull the deputy was forced to shoot it in order to save the life of Tosca and the surrounding community members."
Perez said he had asked the deputies to Taser his pit bull, but one of the deputies instead shot it in the head at close range with an assault rifle.
"Deputies attempted to kick the pit bull away, and pull K-9 Tosca away from the pit bull's attack," said Sheriff's Capt. Mike Parker. "Deputies were very concerned that if further alternate methods were used, and were unsuccessful in immediately stopping the pit bull's vicious attack, K-9 Tosca could have been killed, and the pit bull could have then turned its attack on nearby community members and deputies.
Witnesses said the dog limped back to its home before collapsing in the driveway.
Perez, who has hired an attorney, said what upsets him most is how the situation was handled.
"They don't apologize. They saw their dog was more important to them than my dog," he said. "They're not taking responsibility for it."