Police have identified the perpetrator of an attack in Nice, France, who has killed at least 84 people attending a 14th July firework display.
The perpetrator had weapons and hand grenades in the back of his truck.
Naturally, there is interest in who this person was. An Islamic petty criminal, known to the Police but apparently not to the security services.
In predicting intelligence we are guided by the indifference of the indicator. Any test will do, formal or informal, if it reliably distinguishes one person from another, and has real life predictive value.
In predicting mass violence we should also follow the indifference of the indicator. Muslim men, probably with a criminal background, watching lots of jihadi videos and sermons, recently becoming devout, and probably subject to some random change in personal circumstances which would otherwise not be significant. Noisy data, and hard to find the signal in time to do anything about it. More potential perpetrators than there are teams to follow them.
President Hollande has just told France they will have to get used to terrorist attacks. It would be good to have a Plan B.