SPRINGERVILLE, Ariz. — Four more dead horses have been found, bringing the total to 16 found dead since October 2018, According to the Apache-Sitgreaves National Forest.

U.S. Forest Service officials say at least 10 of the dead horses have evidence of gunshot wounds. Five of the hoses have undetermined causes of death because their bodies were significantly decomposed. One died of blunt force trauma, most likely from a motor vehicle collision. 

This began in October 2018 when two horses were found dead with gunshot wounds to the neck. 

The Forest Service says the investigation into the deaths of these horses can be complex because if it's determined a horse died from a gunshot wound, there must be a "rock solid" burden of proof for court. 

Twelve of the 16 horses were found outside of the Heber Wild Horse Territory near Roads 144, 146, and 50. 

The four horses found on Feb. 7 were discovered inside the Heber Wild Horse Territory near Forest Service Road 300. 

RELATED: Two horses shot dead in Apache-Sitgreaves National Forest

Forest Service law enforcement says it is delegating more resources to these ongoing investigations, which includes working with the Navajo County and Coconino sheriff's offices, using more resources for autopsies of the horses, expanding law enforcement presence in the area and using drones to monitor the area.

The Forest Service has also been into contact with the U.S. Attorney's Office building a potential case if the suspect(s) are found.

Anyone with information is asked to contact the Navajo County Sheriff’s Office tip line at 1-800-78CRIME.