An Arnold, Missouri, Police K-9 died Wednesday after he was left in a patrol vehicle and the air conditioning failed, police say.

 K-9 Vader was found suffering from heat exhaustion by his handler and immediate transported to a veterinary clinic.

 He showed “signs of improvement” at the clinic, the Arnold Police Department said on Facebook. He was then transported to another clinic for round-the-clock care. “Unfortunately, we learned (Wednesday) night that there were no further treatments available for Vader and he succumbed to his injuries,” police said.

Vader was four years old.

The department said all of its 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, the heat alarm system failed to activate.”