The attacker, identified to CNN by law enforcement sources as Sayfullo Habibullaevic Saipov, is accused of renting a truck and using it to mow down bicyclists in lower Manhattan, a few blocks from the rebuilt trade center. Eight people were killed.
Terrorists, like school shooters, learn from other attacks. And no tactic has spread more quickly among terrorists in the West than the use of trucks and other vehicles
to carry out mass casualty attacks.
What was once a rarely used tactic has now become a tactic of choice for terrorists who are living in the West, because these attacks simply require the rental or purchase of a suitable vehicle and access to crowds of people.
Since 2014 there have been 15 vehicular attacks in the West by jihadist terrorists, including Tuesday's attack in Manhattan, according to a count by New America, a nonpartisan research institution. Such vehicular attacks have proven quite lethal, killing 142 people in the West since 2014, including the eight who died in Tuesday's attack.
Witnesses on Tuesday heard the alleged perpetrator shouting "Allahu Akbar!" "God is Great!" during the attack, a slogan that jihadist terrorists often use when they are carrying out an operation.
Saipov, the suspect in the Manhattan attack, is from Uzbekistan. He came to the United States in 2010. According to a law enforcement source, a note was found near the truck used in the attack claiming that it was carried out in the name of ISIS.
Since late January, the Trump administration has proffered three versions of the travel ban
for citizens coming from a total of 10 countries. Uzbekistan is not one of these 10 countries and none of the lethal terrorist attacks in the United States since 9/11, nor 9/11 itself, was carried out by the citizens of the countries targeted by the travel ban.
ISIS called for vehicle attacks
While al Qaeda in the Arabian Peninsula, based in Yemen, had called for vehicle attacks in the West beginning in 2010, it was really only when ISIS leaders called for such operations three years ago that they began to occur frequently.
Although the vast majority of these vehicle rammings since 2014 have been the work of jihadist terrorists, the tactic has also been used by far-right terrorists. For instance, a terrorist rammed his car into an people protesting white nationalists in Charlottesville, Virginia, in August, killing a woman. Palestinian terrorists have also used vehicle attacks frequently against Israeli targets.
For terrorists, vehicular attacks have a number of advantages: They don't need to draw attention to themselves by buying weapons or chemicals suitable for bomb-making or by going overseas for training.
These attacks are also simple to mount and largely unstoppable, because closing access to vehicles to anywhere there are crowds would be an impossible task in crowded Western cities.
Among the other victims of vehicular attacks were the 14 people killed in August when a van mowed down people in a popular tourist area in Barcelona, Spain; the June attack on London Bridge that killed 8, the April attack in Stockholm, Sweden, that killed five; the March attack on London's Westminster Bridge that killed five, and the December 2016 attack at a Christmas market in Berlin, Germany, that killed 12.
The most lethal attack occurred in Nice, France, on July 14, 2016, when a terrorist rammed his truck into crowds celebrating the anniversary of the French Revolution, killing 84 people.
What can be done?
One way to defend against car and truck attacks is to restrict traffic around high profile, crowded events. The New York Police Department already does this around events such as the Macy's Thanksgiving parade. But this wouldn't have prevented Tuesday's attack, because the victims were ordinary New Yorkers traveling through the city on an ordinary day.
Another approach is to try to enlist peers and family members to come forward, since they are the most likely to see signs of radicalization and also, even, attack plotting.
CORRECTION: This story has been updated to reflect the note claiming the attack was made in the name of ISIS was found near the truck.