Officers were on their way with another police dog to catch a suspect when they left Nitro in the car.
Police say the air conditioner in the K-9 unit stopped working, causing Nitro to overheat.
The Stockton Police Department later tweeted a photo of two girls who felt sorry about Nitro and tried to cheer up officers with cookies.
2 young girls who felt sorry for the loss of Nitro brought cookies & cards to the Police Department this afternoon. pic.twitter.com/d1pwd03OXD— Stockton Police Dept (@StocktonPolice) July 1, 2015