The drug-sniffing dog had to be euthanized after it was left in a squad car outside DPS headquarters in Tucson for more than an hour in mid-July.
The Arizona Daily Star says Tucson police conducted the criminal investigation of Officer Korey Lankow.
They say Lankow was en route to a crash in another vehicle when he realized the K-9 was left in the other car and turned back around to retrieve him.
Police presented the case to the Pima County Attorney's Office, which declined to pursue felony charges against Lankow.
The Tucson City Attorney's Office now will determine whether Lankow will face misdemeanor charges in the case.
Information from: Arizona Daily Star, http://www.azstarnet.com