Six more horses have been found shot and killed in Floyd County, Kentucky, bringing the total number of dead horses to 20, a sheriff's sergeant and horse rescue group said Monday.

The dead horses range from foals to full grown horses, some of which were pregnant, and all appear to have died from gunshot wounds, Floyd County sheriff's Sgt. Kevin Shepherd said.

All 20 have been found throughout a former strip mining area. Dumas Rescue, an animal rescue group, is helping lead the search for more of the free-roaming herd that inhabits the area, its president, Tonya Conn, told CNN.

She said it's a remote area, and that's making the search difficult. They've been able to search about 4,000 acres a day, covering 80% of the area since December 16.

The search is expected to end this Saturday, Conn said.

Searchers have found the bodies spread out. Conn said she believes that when the shooting began, the horses scattered, then the shooter tracked them down and killed them.

They've been helping conduct field necropsies, Conn said, as they have been unable to move most of the horses.

Conn says the herd had about 35 horses in October. Because most of them were horses that had been abandoned by their owners, the horses were very approachable to humans, Conn said.

Rescue volunteers had rescued seven horses before the killings started. They believe about six are left following the shootings, Conn said.

Dumas Rescue is working to rescue them, but the rain-saturated ground is making the rescue operation on the old mining access roads treacherous, even impassible, she said.

Sgt. Shepherd said the deaths are under investigation. Officials in Lexington, Kentucky began conducting a necropsy on a foal Monday and hope to find bullet fragments, he said, adding it appears a small-caliber weapon was used to shoot the horses.

The incidents began December 16 when a resident called 911. Some of his horses broke out of a fenced area; he later found them shot to death.

Dumas Rescue is offering a $20,000 reward for information that leads to the arrest of those responsible.

This is the largest use of resources for the organization since it was formed in 1999.

Five volunteers make up Dumas Rescue and they normally foster rescue animals in their own homes before they're transported to no-kill shelters.

Dumas Rescue is currently trying to raise funds for the horses.

The-CNN-Wire

™ & © 2019 Cable News Network, Inc., a WarnerMedia Company. All rights reserved.