Motive, means and opportunity.  

Motive: 1. Adherence to the dark arts, black magick, Crowleyism and Satanism in the belief that it will give them power over others. In short, to practice their spiritual beliefs through deed and words.  

Evidence of this one motive?  

Association with occult practitioners like Abramovic. Occultic symbolism found through associates and other connections. Invoking Moloch. Appreciated artwork that suggests ritualized practice. Precedent of past cases throughout history where satanic rituals were the prime motivating influence for abuse, murder and cannabalism of victims.