Officially, the Wagner Group is a Russian private paramilitary contracting organization whose business is to provide mercenaries for hire. A number of Wagner Group mercenaries have been active in Syria.
In July 2017, Wagner Group mercs filmed themselves brutally torturing, beheading, dismembering and incinerating a Syrian man accused of desertion.
Identified as Muhammad Abdullah al-Ismail, the victim is bludgeoned on hands and feet with a sledge hammer, has his genitals blown up with a firecracker and gets shot in non-vital parts of the body to induce pain and suffering.
After the period of torture, the victim is beheaded with a short blade and an entrenching shovel. The same tools are used to dismembered him. The mutilated corpse is then suspended upside down from a frame, doused with a flammable liquid and set on fire.
Additional information from @natural-selection-2:
I took a closer look to the explosive device they use to torture. It is a disassembled detonator from a Russian hand grenade. Around 01:34 min you can see the safety pin get pulled.
One of the mercs is known as Stanislav Yevgenyevich Dychko. He was born in 1990. Joined Wagner shortly after a discharge from Russian interior ministry. He is currently living a normal life in freedom… There are no charges against him.
Props to Best Gore member @natural-selection-2 for the video: