I don’t have much backinfo, beside the fact that the video is from Brazil. But the celebratory “V” handsign, which the killers boastfully perform, is associated with the Comando Vermelho (Red Command) gang.
The remains shown off in the video are of a young man who was decapitated and dismembered by the gang. It is often done to rival gang members, such as those affiliated with Família do Norte or Primeiro Comando da Capital.
Props to Best Gore member @nikish for the video: