As with the killing of 49 people in a nightclub in Florida last month, investigators will want to establish the degree to which Isis or any other group might have been involved as soon as possible. This is not a mere detail but crucial to understanding the continuing threat.
There is a vast range of possibilities: from direct commission, organisation and execution through to the most tenuous connection via ideological inspiration over the internet. There are reports that the attacker in Nice was a 31-year-old French citizen of Tunisian origin who was known to police, but not to intelligence services.
French authorities – like counterparts around the world – have learned that the most lethal attacks in their country have been perpetrated by individuals or networks with connections to outside organisations.
Mohamed Merah, who killed seven in a shooting spree in 2012, was initially described as a lone wolf but found to be connected to a breakaway al-Qaida faction. Those who attacked Charlie Hebdo magazine last year had a tenuous link to al-Qaida in Yemen. The more recent strikes, including those in November last year and in Belgium in March, involved a well-established network linked to Isis.