Officer Robert Price was placed on paid administrative leave Thursday, which is standard procedure when an officer is charged.
The Adams County District Attorney's office spent three weeks investigating the shooting death of a dog named Chloe.
A neighbor took cell phone video of the dog's death, which is now a key piece of evidence in the criminal investigation.
Chloe's final moments are too painful for the dog's owner, Gary Branson, to watch.
"This makes no sense. Just a waste of a good life," Branson said.
Branson left Chloe with a family member in Commerce City last month, and she got loose on Nov. 24. Neighbors called Commerce City police, reporting an aggressive animal.
WATCH: Raw video of police killing dog [Graphic]
As police arrived, a neighbor took cell phone video from an upstairs window. The video shows officers had Chloe restrained, when witnesses say the dog was scared and tried to run away.
Officer Price fired five shots, killing the animal.
"I really can't find the words to describe it," Branson said.
Commerce City communications director Michelle Halstead says the police department brought in the Adams County District Attorney's office three days after the shooting, as community outrage grew over Chloe's death.
"We're making sure that there's an independent, transparent review of our actions," Halstead said.
A Facebook page for Chloe has more than 2,700 likes as supporters posted pictures and messages of support.
Vigils and protests were also held for the dog.
"Our thoughts have been and continue to be with the owner during this very difficult time," Halstead said.
A statement from the DA's office says a three week review led to a felony charge of aggravated cruelty to animals.
The statement says investigators interviewed 15 additional witnesses, collected new evidence, and attended the necropsy of the dog which included an expert in gunshot wounds.
Commerce City police are bringing in the Douglas County sheriff's office to investigate if any city policies were violated.
"Commerce City is committed to making sure our employees are well trained and prepared to respond to unpredictable emergency situations, while ensuring the safety and well being of our community. We look forward to Douglas County's objective conclusions and will work with the incoming police chief to take the appropriate next steps to positively move the police department forward and prevent such incidents from occurring in the future," Halstead said in a statement.
Officer Price is due in court on the animal cruelty charge in January.
At his home in Pueblo, Branson says it's hard to live with the pain of losing Chloe.
"The closest thing I've come to losing a family member. Every time I turn around she was there and now she's not," Branson said.
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