From the FBI's open briefing, an article by a psychiatrist, with numerous references; his slim bio:
Dr. Meloy is a clinical professor of psychiatry at the University of California, San Diego, and a consulting forensic psychologist to the FBI
What is the research doing?
The author and his colleagues are in the process of analyzing data concerning individual terrorists—religious and secular motivations—in North America and Europe. In a study of 22 European terrorists, five warning behaviors (pathway, fixation, identification, energy burst, and last resort) were found in more than 90 percent of the cases. In another larger study of 111 lone-actor terrorists in the United States and Europe, pathway, fixation, identification, and leakage were present in 77 to 96 percent of all subjects. Such efforts will demonstrate whether these behaviors have value as part of an instrument for risk-assessment efforts.
Link:https://leb.fbi.gov/2016/april/persp...dual-terrorist