A team of investigators are looking into the dog's death.
Wilfred Europe III, the deputy who pulled the trigger, has been reassigned and is no longer on patrol.
This is not the first fatal shooting involving Deputy Europe.
Deputy Europe shot and killed 40-year-old Don Cambron last February during a traffic stop.
Cambron's friend Tim Collins, who was in the car, told 9NEWS Cambron was not reaching for a pellet gun, which is what Deputy Europe told investigators before he was cleared of any wrongdoing.
"There's no rationale there at all. Except that a cop got trigger happy," Collins said.
On Thursday afternoon, Adams County deputies returned to the workshop where the dog shooting occurred to collect evidence.
I'm glad that they're taking the effort to come out and investigate the way they should have initially," dog owner Jeff Fisher said.
Fisher says two deputies showed up at the wrong address Monday night while investigating a security alarm.
Ziggy was a 35 pound, 8-year-old blue heeler/border collie mix who Fisher says was not aggressive.
He says two Adams County deputies forced their way into Fisher's business, startling his dog which ran outside.
"He turned to come back to me. And the police officer opened fire. He ran past the police officer at the door. He just wanted to see who it was. And the police officer shot him 3 times," Fisher said.
Fisher says Ziggy was about 15 feet from the deputy who opened fire.
"I'm yelling, 'you shot my dog. You shot my dog.' And the police officer says, 'you need to calm down. You can get a new dog,'" Fisher said.
Fisher described the whole situation as "surreal" and claims Ziggy was not being aggressive.
"That dog was my best friend," Fisher said. "They never informed me they were police officers. They shot him on a concrete slab. It's never going to be the same. I raised that guy since he was 6 weeks old."
"There's some pretty suspect things in Officer Europe's history," said attorney Jennifer Edwards with the Animal Law Center.
Edwards represents several Adams County dog owners whose pets were killed by law enforcement.
In November, Commerce City police officer Robert Price shot and killed a dog named Chloe.
Home video shows Price shooting the dog five times when she was already restrained.
Price faces a felony charge of animal cruelty and his arraignment is scheduled for Tuesday, Jan. 22.
Price is on paid administrative leave pending the outcome of the criminal case against him.
Before Chloe, there was Zoey, gunned down in her family's driveway by another Commerce City officer.
The officer was checking on a 911 hang-up call and said three "vicious dogs" threatened her.
She shot the Agazio family's dog, Zoey.
Edwards sued on behalf of the family, and lost.
Last August, a jury ruled the use of deadly force was justified, but also found killing someone's pet violates their constitutional rights.
"I just hope there's justice for Ziggy, Chloe, Zoey. I hope that one of these departments will take the lead and change their policies, procedures, and training," Edwards said.
In regards to the investigation into Ziggy's death, Adams County Undersheriff Roger Engelsman spoke to 9NEWS by phone.
"This is a very, very serious investigation for us which we are conducting as quickly as possible so that we can share the results when it's complete," Engelsman said.
Fisher hopes Ziggy's death will change things in Adams County, even as he struggles with the loss of his best friend.
"He was a good boy. He was my good boy. That's my memory," Fisher said.