Stirton and his crew, along with a group of rangers, set out for where the murdered gorilla had been reported - walking five hours through dense jungle.
When they arrived, they found carnage. A total of seven gorillas had been slaughtered, including one pregnant female. Bullet holes riddled the body of Senkwekwe, the male silverback.
Solemnly, the rangers began to cut down small saplings to carry the gorilla's bodies.
What struck Stirton most, as the brokenhearted rangers prepared to carry the murdered apes to a special burial ground, was the absence of any talking at all. "This was all very silent," he said.
It took the rangers more than seven hours to carry the gorilla's bodies to their final resting place.
It was immediately clear that the gorillas hadn't been killed by poachers, because their bodies were intact, but rangers couldn't figure out why so many had been shot.
It wouldn't come out until later that the gorillas had been murdered by people involved in the illegal charcoal trade - who were after the valuable hardwood trees in Virunga's protected gorilla area.