On Thursday night, Mohamed Lahouaiej Bouhlel drove a truck through a group of people celebrating Bastille Day in Nice, France, killing 84 people and injuring more than 200 others. Now a few days later, the Islamic State, also known as ISIS, has officially claimed responsibility for the attack on the seaside promenade. 

According to the New York Times, ISIS released the following statement from a social media account associated with the Amaq News Agency, the Islamist militant group's official news outlet: "The man behind the running-over operation in Nice, France, is a soldier from the Islamic State, and he carried out the attack to answer the calls for targeting the nationals of countries in the coalition that is fighting Islamic State." 

While this development in the story is certainly major, it must be taken with a grain of salt, as ISIS has previously claimed responsibility for attacks it did not actually plan or have any role in carrying out. For one, Mr. Lahouaiej Bouhlel was never suspected of terrorist activity and came off as more of a loner to the people who interacted with him. "The individual who committed this absolutely despicable, unspeakable crime was not known by the intelligence services, as he had not stood out over the past years—whether through court convictions or through his activity—for support of radical Islamist ideology," Interior Minister Bernard Cazeneuve said. 

Mr. Lahouaiej Bouhlel's father said that his son suffered from depression but that he had barely any associations with religion and that "he didn't pray, he didn't fast, he drank alcohol, and even used drugs" in a statement to Agence France-Presse on Friday night. He added that his son had major mental health issues between 2002 and 2004 that led to a nervous breakdown. 

Right-leaning parties have accused the French government of being remiss in security measures leading up to the attack, but Stéphane Le Foll, the chief government spokesperson, has rejected that criticism. "When you are talking after the fact, you can always find solutions," he said. Le Foll added that security on the night of the attack was just as stringent as it was during the Euro 2016 soccer tournament, which ended just four days before the attack in Nice. 

Today marks the first of three days of national mourning in France.