When Mr. Rahami was captured during a shootout with the police on Monday, the authorities found a notebook, pierced with a bullet hole and covered in blood, expressing opinions sympathetic to jihadist causes, according to a law enforcement official who agreed to speak about the investigation only on the condition of anonymity.
In one section of the book, Mr. Rahami wrote of “killing the kuffar,” or unbelievers, the official said. Mr. Rahami also praised Anwar al-Awlaki, Al Qaeda’s leading propagandist, who died in a drone strike in Yemen, as well as the soldier in the Fort Hood shooting, one of the deadliest “lone wolf” attacks inspired by Al Qaeda.
Killing the kuffar isn't a "perversion of Islam". It is Islam.
Islam settles religious disputes, internally or externally, with murderous violence.