When mass murders happen in a place like the US, despite the fact that they are no more prevalent than most countries and murders have plummeted as gun ownership rose, the simplistic answer is 'guns' - when murders happen in Canada or France, where gun ownership is heavily restricted, the answer is not so convenient. 

It may not be guns forcing people to kill people, it may be attachment to an 'overvalued idea' - and it may become more common.

Zehaf-Bibeau, the Islamist convert who murdered a Canadian military reservist on duty in Ottawa, represents a type of attacker rarely discussed--a person so obsessed with an overvalued idea that it defines their identity and leads them to commit violence without regard for the consequences.

David Pope's cartoon shows an example of the overvalued idea of misguided sociopaths. Posted on Twitter.

The terrorists in France were just that, and as has been noted in American discussions on gun control, criminals and terrorists will get rocket launchers and machine guns no matter how much law-abiding citizens are restricted, but since they were French they also fit the description of people acting on overvalued ideas. A new paper in Violence and Gender tries to make the case that this is an emerging, and likely growing, phenomenon.

Author Matthew H. Logan, PhD, a 28-year veteran officer with the Royal Canadian Mounted Police (RCMP), as well as an RCMP Criminal Investigative Psychologist (ret.), Ontario, Canada, explains that these killers do not always work alone, stating that "in the future I believe we will see more 'packs' of these wolves as they unite on common beliefs and themes."

"The violence we witnessed in Paris just days ago shook the world," says Violence and Gender Editor-in-Chief Mary Ellen O'Toole, PhD, Forensic Behavioral Consultant and Senior FBI Profiler/Criminal Investigative Analyst (ret.). "It was coldblooded, purposeful, and seemingly without remorse, driven by a unique self-righteous ideation of the killers. Dr. Matt Logan explains the 'motivating mindset' of young male offenders, sometimes loners and sometimes part of a group, whose 'overvalued ideas' combined with their own psychopathology is what motivates them to engage in this type of terror. 'Overvalued ideas do not constitute mental illness,' according to Dr. Logan, which makes this senseless, savage violence seem even more chilling and despicable."