A Missouri police dog died from heat exhaustion this week after officials said the animal was left in a patrol vehicle and its air conditioning reportedly failed.

Vader, a German Shepherd with the Arnold Police Department, died Wednesday from heat exhaustion, the agency reported.

He was 4.

"We lost a member of our K-9 family in a tragic accident," the department posted on Facebook Thursday.

According to the agency, located in a suburb of St. Louis, Vader's police handler left the dog in a patrol vehicle with the air conditioning running, a "necessary and common practice when the K-9 partner is not actively engaged in police work."

Arnold police Chief Brian Carroll identified Vader's handler as Officer Tim Mayberry. On Friday, Carroll told USA TODAY Vader was put into service in 2021.

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Police K-9 died from heat exhaustion

When Vader’s partner returned to the vehicle, they found discovered its air conditioning system malfunctioned.

Vader was immediately transported to a local veterinarian clinic where initially, police reported, he showed signs of improvement.

The dog was then taken to a 24-Hour clinic for further treatment.

"Unfortunately, we learned last night that there were no further treatments available for Vader and he succumbed to his injuries," the agency wrote.

Carroll would not say whether the officer was responding to a call when the incident took place citing an active pending investigation into the dog's death.

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Police: Vehicle's heat alarm system failed

Police said all of the department's K-9 vehicles are equipped with a system "that notifies the handler by phone, activates the emergency lights and siren, sounds the vehicle horn, activates cooling fans, and rolls down the vehicle windows, if the vehicle temperature increases to a certain level."

In this instance, police said, the heat alarm system failed to activate.

Vader's death remains under investigation by the department.

"Please keep Vader’s handler, his family, and the members of the APD in your thoughts and prayers as we mourn the loss of our K-9 partner," a police spokesperson said.

Natalie Neysa Alund is a senior reporter for USA TODAY. Reach her at [email protected] and follow her on X @nataliealund.