Police arrived to the 300 block of Mission Road after receiving a call that a 60-pound pit bull had chased a client from the Glendale Adventist Drug and Alcohol Center into the building and was scratching at the door, officials said.
The clients feared being bitten and didn't want to exit the building, prompting calls to the police, Lt. Gary Montecuollo said. No one was bitten during the incident.
Two officers and a police sergeant saw the pit bull near the building and parked on one end of the block to assess the situation, he said. It was then that the dog slanted its ears back and began sprinting toward the officers.
Officers first shot the dog with a rubber bullet, but it didn't stop and continued running toward them. That's when they used regular ammunition, killing the dog, Montecuollo said.
"Unfortunately, officers killed the dog, but stopped the threat," he said.
Animal control officers cited the owner for not having a license for the dog, which had been living in the city for eight years, said Ricky Whitman, a spokeswoman for the Pasadena Humane Society, which services Glendale.
A second dog belonging to the same owner, whom police identified as 28-year-old Priscilla Chacon, was also found roaming the neighborhood.
Chacon could not be reached for comment.
The owners were also cited for not having a license for the second dog and for failing to restrain the dogs on a leash, Whitman said.
The pit bull had reportedly escaped from the home's yard and terrorized residents for several days.
No one reported the dogs to police before Tuesday's incident, but some residents said the pit bull had been aggressive and nipped at a cyclist, police said.
Neighborhood resident Lillian Lonnon saw both dogs roaming the streets several times. She never had a violent encounter with the dogs, but she said they were clearly aggressive.
"I didn't like that dog," she said of the pit bull.
Police were investigating the incident and a standard internal review had been launched into the officers' actions, officials said.
Whitman said the officers likely had no other choice but to shoot the dog since it didn't react to the rubber bullet.
"[Police] did exactly what they needed to do for their safety and the public's safety," she said.