We detected the nighttime death of a radio-collared three-toed sloth (Bradypus variegatus) with an automated radio telemetry system in a Panamanian moist forest. Forensic evidence collected at the fresh carcass, including five pairs of zygodactyl puncture wounds, and the consumption of only soft tissue, suggests that the predator was a large owl, probably Pulsatrix perspicillata. Telemetry data, feces in the sloths' rectum, and old sloth feces at the base of the tree near the carcass suggest that the sloth was descending to the ground to defecate when it was killed. If correct, this is the first record of P. perspicillata killing such a large prey, highlighting the importance of crypsis, and not self-defense, as sloths' anti-predator strategy. This event also suggests there are high risks for sloths climbing to the ground to defecate, a puzzling behavior with no clear evolutionary advantage discovered yet.