Accused killer Luigi Mangione appears to have been plotting his attack on UnitedHealthcare CEO Brian Thompson for at least three months — penning a desire to take out the head of a medical insurance company in a notebook laden with angry tirades against the industry,

"The target is insurance because 'it checks every box,'" read a passage from a notebook, which was dated Aug. 15, that authorities found with Luigi Mangione, according to the court papers.

Luigi Mangione was charged in a four-count federal indictment that could land him the death penalty if convicted of murder.