(CNN) There have been eight lethal terrorist attacks in Europe since 2014, five of them in France alone, carried out by ISIS or by "lone wolves" inspired by the terror group or by al Qaeda. What do these attacks have in common? The terrorists are almost invariably criminals who have either served time in the French or Belgian prison systems, or they have been convicted for lesser offenses but have avoided jail time. Mohamed Lahouaiej-Bouhlel, who killed at least 84 people Thursday in Nice, France, had a long record of petty crimes. Bouhlel assaulted a motorist last year for which he received a six-month suspended sentence.Peter Bergen: Many of those behind terror attacks in Europe shared criminal backgroundConditions in French prisons incubated the radicalization of many terrorists, he says
_ and Belgian prisons have proven to be universities of jihad. _ has begun to implement new measures, such as separating militants from the general prison population and placing them in solitary confinement so they cannot exert their ideological influence on other inmates.