By Layron Livingston

Mercer County, OH (WHIO/CNN) - Sheriff's officials in Mercer County, Ohio are mourning the loss of a four-legged partner.

A K-9 died Wednesday after his handler left him in a hot patrol car.

When Zak joined the force, springing onto duty back in 2010, he was assigned to Deputy Chad Fortkamp.

"Deputy Fortkamp loved that dog almost like it was his child, so, it's a terrible tragedy," said Sheriff Jeff Grey.

Grey says Zak suffered from a pre-existing heart condition, but it's believed he was overcome by the heat.

"I don't know why we had the dog in the car, you know, why the dog wasn't left at home," said Grey.

We're told Zak is normally brought inside the building or left in his cruiser with the air conditioning running when he's at the office.

His handler, Deputy Fortkamp, was apparently working outside of his normal shift at the office when he discovered the dog dead.

We're told Zak was left in his cruiser with the air conditioning off.

"This incident is not being taken lightly by the sheriff's office. It's not being taken lightly by Deputy Fortkamp. We are going to get to the bottom of it," said grey.

He apologized to the members of the Moose Lodge and the Eagle of Celina. It was their donations that brought Zak to the county in the first place.

Grey couldn't say how long Zak was in the hot cruiser, or if he had water. He says Fortkamp has never been a problem employee and doesn't think his actions were intentional.

This is reportedly the second Mercer County sheriff's dog to die within the last three years.

The sheriff's office is suspending the K-9 program until further notice.

WHIO/CNN