Mohamed Bouhlel

A 31-year-old father of three obsessed with fitness and sex, Mohamed Lahouaiej Bouhlel led multiple lives. His darkest side appears to have been his best-kept secret: a calculated, committed jihadi ready to kill scores of people in a French Riviera rampage.

French authorities detained two more people Sunday and released the estranged wife of the slain Nice truck attacker from custody as they tried to determine whether he had been an Islamic extremist or just a very angry man.

Just hours after a man drove a large truck through a crowd in the French seaside town of Nice, killing at least 84, French President Hollande made a televised address to the nation.

This time, France was supposed to have been better prepared.

The rogue driver who turned a night of fireworks and fun into the worst carnage the French resort city of Nice has seen in decades appeared aloof and menacing to his neighbors and family, while authorities said Saturday that he had recently turned to religious extremism.

—France called up thousands of reserve security forces Friday as authorities tried to determine why a Tunisian deliveryman known only to be a petty criminal took the wheel of a 19-ton truck and plunged through a terrified seaside crowd on Bastille Day, leaving 84 people dead and more than 200 wounded.