"Main perpetrators" refers to the primary people or individuals who are primarily responsible or involved in carrying out a particular action, usually something negative or harmful. Full definition
For this we can thank Carl Paladino and Steve Pigeon, who, along with Steve Casey, are the main perpetrators of «politics as a blood sport» that permeates the local scene. (investigativepost.org)
And why does Shadow Home Secretary Yvette Cooper's statement skate around the central issue: that the main perpetrators of this abuse were Pakistani men? (labour-uncut.co.uk)
Regulatory T cells (Tregs) have an immunosuppressive function and, through a variety of different direct and indirect mechanisms, inhibit effector T cells, the main perpetrator of transplant rejection. (immunology.org)