Zachary Miller was charged with animal cruelty in connection with the death of his K9 partner, Nyx, after the dog was left in his police patrol car for more than six hours. However, the police officer who was with him will not be disciplined.

The affidavit, as reported in local Wyoming newspaper the Casper Star-Tribune, states Miller arrived at the police department at 5:30 a.m. on July 9. He left shortly after with fellow police officer Jake Bigelow (the only other officer on the clock at the time) to respond to a call.

They returned and went inside the station about 6 a.m, leaving the dog in the car, and did not return to the car until about 12:20 p.m. The outside temperature had climbed from 53 to 86 degrees. The officers had also left the car running that entire time. The air conditioning was off and the windows were up.

Mills police chief Bryon Preciado said, “It’s not normal to leave a car running that long.” He added that police dogs are allowed inside the station.

Miller was busy training Bigelow on patrol-duty procedures during the time the dog was in the car. Miller is no longer a training officer.

Miller was in circuit court Friday, where he plead not guilty. If convicted, he faces a maximum penalty of six months in jail and a $750 fine.

Preciado said Miller will remain employed at the police department. Miller was suspended with pay for one week starting the day Nyx died. He is currently on paternal leave.

Bigelow will not be disciplined. The reasons the officer, who accompanied Miller the entire duration of the incident, will escape punishment have not been disclosed.

This fatal mistake surprises Miller’s co-workers, as Miller was seen as “pro-active” and was just awarded “Officer of the Year” in his department in 2013.

Miller had been Nyx’s handler for two years.

Nyx, a black lab who was trained to detect drugs, had been with the Mills police department since 2006 as their first and only police dog. He was 10 years old.

The department plans to install temperature alarms in the K9 patrol car before they acquire a new police dog. The alarm will be rigged to a key fob to be carried by the handler so as when the temperature in the car goes above or below a certain level, the alarm will sound.