Police said the dog, named Ozzy, and his handler were both off duty when this happened on Aug. 14. The dog was inside the officer's department-issued K-9 vehicle, and it was the handler who found the dog, LBPD spokeswoman Shaunna Dandoy told the Long Beach Post.
Dandoy told the Long Beach Post that the preliminary results from a local veterinarian determined the cause of death to be heat related.
"All circumstances surrounding the death, including possible equipment or mechanical failures, are being reviewed,'' Dandoy said.
No further information was immediately available. Long Beach police say the whole incident is now being reviewed.
City News Service contributed to this report.