US

Experts confront multiple explanations for surge of killings

  • FILE - In this Friday, July 14, 2016 file photo, police stand by as medical personnel attend a person on the ground, right, on the Promenade des Anglais in Nice, southern France, next to the lorry that had been driven into crowds of revelers late Thursday. The relentless series of mass killings across the globe poses a challenge for experts trying to analyze them without lapsing into faulty generalizations. Terms like contagion and copycat killing apply in some cases, not in others, they say, and in certain instances perpetrators' terrorist ideology intersects with psychological instability. (AP Photo, File)

    FILE - In this Friday, July 14, 2016 file photo, police stand by as medical personnel attend a person on the ground, right, on the Promenade des Anglais in Nice, southern France, next to the lorry that had been driven into crowds of revelers late Thursday. The relentless series of mass killings across the globe poses a challenge for experts trying to analyze them without lapsing into faulty generalizations. Terms like contagion and copycat killing apply in some cases, not in others, they say, and in certain instances perpetrators' terrorist ideology intersects with psychological instability. (AP Photo, File)  (The Associated Press)

  • FILE - In this Friday, July 22, 2016 file photo, police escort people who leave the Olympia mall after shots were fired in Munich, southern Germany. The relentless series of mass killings across the globe poses a challenge for experts trying to analyze them without lapsing into faulty generalizations. Terms like contagion and copycat killing apply in some cases, not in others, they say, and in certain instances perpetrators' terrorist ideology intersects with psychological instability. (AP Photo/Sebastian Widmann, File)

    FILE - In this Friday, July 22, 2016 file photo, police escort people who leave the Olympia mall after shots were fired in Munich, southern Germany. The relentless series of mass killings across the globe poses a challenge for experts trying to analyze them without lapsing into faulty generalizations. Terms like contagion and copycat killing apply in some cases, not in others, they say, and in certain instances perpetrators' terrorist ideology intersects with psychological instability. (AP Photo/Sebastian Widmann, File)  (The Associated Press)

  • FILE - In this Saturday, July 23, 2016 file photo, people mourn with flower tributes near the Olympia shopping center where a shooting took place the day before in Munich, Germany. The relentless series of mass killings across the globe poses a challenge for experts trying to analyze them without lapsing into faulty generalizations. Terms like contagion and copycat killing apply in some cases, not in others, they say, and in certain instances perpetrators' terrorist ideology intersects with psychological instability. (AP Photo/Jens Meyer, File)

    FILE - In this Saturday, July 23, 2016 file photo, people mourn with flower tributes near the Olympia shopping center where a shooting took place the day before in Munich, Germany. The relentless series of mass killings across the globe poses a challenge for experts trying to analyze them without lapsing into faulty generalizations. Terms like contagion and copycat killing apply in some cases, not in others, they say, and in certain instances perpetrators' terrorist ideology intersects with psychological instability. (AP Photo/Jens Meyer, File)  (The Associated Press)

The series of mass killings across the globe poses a challenge for experts trying to analyze them without lapsing into faulty generalizations. Terms like contagion and copycat killing apply in some cases, not in others, they say, and in certain instances perpetrators' terrorist ideology intersects with psychological instability.

Some of the attacks, such as the assault on multiple targets in Paris last November, were elaborately planned operations by Islamic State adherents. However, they may have contributed to other attacks by troubled individuals with no established ties to the militant group.

J. Reid Meloy, a San Diego-based forensic psychologist who has served as a consultant to the FBI's Behavioral Analysis Program, said some of the attackers appear to have identified with Islamic State as an outlet for their own seething emotions.