This pattern of rationalization and decreased responsibility is "very common, " says Patrick Lyden, MD, the chair of the department of neurology at Cedars-Sinai Medical Center, in Los Angeles.

CNN: Aging workforce means dementia on the job could rise

There's not always a claim of responsibility in attacks like this, but this does follow the pattern of Madrid in 2004.

NPR: Investigators Cautious on Assessing Blame for Attacks