A person who defecates in a public place. [poop + perpetrator]
In the past several weeks, an unknown individual or group, who students have dubbed the ‘poopetrator,’ has repeatedly defecated in students’ laundry, leaving many fearful about the safety of their clothes.
—Adrian Rodrigues, “Police probe Saybrook laundry incident,” Yale Daily News, October 2, 2013
Director of Parks and Recreation Dr. Michelle Grigore told the Board of Parks and Recreation Tuesday night that closings indicate how seriously the staff takes the incidents. She said time was taken to attempt track down the “poopetrators,” which drew a chuckle from board members.
—Harold Brown, “‘Poopetrators’ cost BG pool about $5,000,” Sentinel-Tribune, July 24, 2013
During the night, certain perpetrators were sneaking onto play equipment in parks and school yards and leaving deposits....
The city stepped up surveillance of the park, which is just across the street and down the hill from the Police Department. It installed lights and a security camera. But it couldn’t catch the poopetrators.
—Susan Lampert Smith, “Police aid nabs park befoulers by working turd shift,” Wisconsin State Journal, December 10, 2004
Here's an earlier usage where the poopetrator is a dinosaur that left a coprolite (fossilized feces):
Identifying what Chin calls the “poopetrator” is probably the most difficult part of studying coprolites.
—David Tenenbaum, “Fecund Feces,” The Why? Files, May 3, 2001