A Wyoming police officer is being charged with animal cruelty after his police dog was left in a hot patrol car for hours and died, according to the Casper Star Tribune.

Four-year Mills Police Department veteran, Zachary Miller, is being charged with misdemeanor animal cruelty for the death of Nyx, a female drug detection dog.

According to an investigator's affidavit from the Natrona County Circuit Court, Miller left Nyx in his patrol car for more than six hours outside the police department. Though the car was running, the air conditioning was off and the windows were not rolled down, according to the Star Tribune.

Mills police chief Byron Preciado said there isn't a policy on the time an officer can leave police dogs in patrol cars but he doesn't agree with Miller's actions.

"It's not normal to leave a car running that long. I'm not justifying it. He shouldn't have been here that long," said Preciado.

Miller arrived at the police department on July 9 at 5:30 a.m., according to the affidavit. Miller and officer Jake Bigelow, who Miller was training at the time, left to respond to a call and got back to the police department with Nyx around 6 a.m.

But instead of bringing Nyx inside - Preciado says dogs are allowed inside the station - the two officers left Nyx in the car without water and went inside the department. The officers did not go back to the car until about 12:20 p.m., according to the Star Tribune. The temperature outside raised from 53 to 86 degrees, according to the affidavit.

Miller said he yelled at Bigelow for not leaving the air conditioning on, though he does acknowledge Nyx was his responsibility, according to KCWY13.

Nyx, a 10-year-old black lab, was with the department since 2006. She was their first and only police dog.

Miller had handled Nyx for two years and Nyx even lived with his family and went on family vacations with the Miller's, according to the Star Tribune.

Nyx worked for Casper Police, Wyoming Highway Patrol, the Natrona County Sheriff's Officer and the Division of Criminal Investigation, according to Preciado.

"It's a mistake he's going to have to pay for. He's going to be disciplined through our department," Preciado said.

Miller pleaded not guilty to the charge this morning. If convicted, he faces a maximum penalty of six months in jail an a $750 fine, according to the Star Tribune.

"If he violated the law then he should be held accountable jut like anybody else," Preciado said.

Though Miller is still employed by the Mills police department, Preciado says he is not on active duty because he is on paternal leave. Miller was also suspended with pay for a week after Nyx's death but returned to work after an internal investigation by the department, according to the Star Tribune.

The other officer is not being charged since he was being trained by Miller.

Before this, Miller never faced disciplinary action by the department. Actually, Miller was awarded "Officer of the Year" by the department in 2013 and was known as "pro-active," Preciado said.

Preciado says before the department gets a new police dog, heat alarms will be installed in K9 patrol cars.

Nyx was buried on Miller's property.

"It's a tragedy," said Mills Mayor Marrolyce Wilson.