Arizona police have arrested a 59-year-old man from Seattle for discarding skulls and limbs from at least five people in a dense forest near Prescott, Arizona.

Walter Mitchell, who had recently closed a firm called Future GenX that bought and sold cadavers for medical research and had once described himself in an article on the body-part trade as a “veteran body broker,” was taken into custody in Scottsdale. The body parts are all believed to belong to people who donated their cadavers to scientific research.

Mitchell was charged Wednesday with 28 counts of improperly moving human remains, which is a Class 5 felony.

Authorities first learned about the grisly remains Saturday when a hunter reported finding two intact heads with gauze “puppy pads” commonly used in medical research. Authorities later located three more heads and a pile of assorted limbs in another part of the forest.

Sheriff Scott Mascher told local media that they had initially opened a serial-killer homicide investigation, but after determining that the “puppy pads” were tied to anatomical research, they changed tack. “This situation is unimaginable,” Mascher wrote on a Facebook post. “I am so sorry for the families whose loved ones were donated to research and treated in such a horrific fashion.”

Authorities say Mitchell drove 1,425 miles from Seattle with the heads and limbs in his car before scattering them in a forest near Prescott sometime earlier this year. He was living in Scottsdale at the time of his arrest.

“The disrespect shown to the deceased in this case by those who were charged with caring for their remains is abhorrent and intolerable,” Yavapai County Sheriff David Rhodes said in a statement.