Investigators searching for dead horses on land once owned by the family of a suspended (South Carolina) state official on Friday picked through a South Carolina field marking spots where they found bones or thought shallow graves were dug for the animals.

It was not clear how many horse bodies were buried or scattered over the Sumter County property once owned by Assistant Agriculture Commissioner James Trexler and his mother and brother.

Authorities have marked at least 15 spots where bones were either easily visible on top of the ground, protruding from small earthen mounds, or at the sites of sunken rectangles roughly 6-by-4 feet.

All three Trexlers were charged this week with abusing horses that Humane Society investigators say were malnourished at two fields in Richland County, which borders western Sumter County (in South Carolina)