NEW YORK — More than two days after the driver of a pickup truck crushed pedestrians in a bike lane in lower Manhattan, at least four clues have emerged showing the radicalisation of the suspect, Sayfullo Saipov.

While it remains unknown if the suspect was speaking to the terrorist group or being guided by it, pieces of paper and two cellphones at the scene provide a window into his familiarity with the terminology of the Islamic State (IS), also known as ISIS.

INVOKING A SLOGAN

Feet from where the truck came to a stop Tuesday afternoon (Oct 31), police recovered sheets of paper bearing a message written in Arabic and English, “It will endure,” they said, referring to IS, according to the criminal complaint against Saipov.

The phrase is familiar to followers of the group. Throughout the territory it once held in Iraq and Syria, IS left one Arabic word: baqiya. It was printed on billboards and spray-painted on the buildings it confiscated. Enter a home formerly occupied by one of the terrorist group’s emirs, and you find it scrawled in marker on the walls.

You can even find it etched into the desks they used, like teenagers carving their initials on a picnic table.

It means “remaining” or “enduring,” and it is the terrorist group’s slogan, dating to when it was still an affiliate of Al Qaeda.

A senior law enforcement official, who had been briefed on the investigation into the New York attack, said the phrase appeared more than once in the note. “There’s some stuff in the beginning and then there’s the repeated, ‘The Islamic State will endure forever,’ or ‘will last forever,’ you know, three times, in Arabic,” he said, speaking on condition of anonymity because the investigation is continuing.

ADHERING TO DIRECTIONS

The IS’ magazine, Rumiyah, provided detailed guidance on truck attacks in an issue published in November 2016. The group encouraged supporters to keep driving the car for as long as possible. “To ensure the most carnage over upon the enemies of Allah, it is imperative that one does not exit his vehicle during the attack. Rather, he should remain inside, driving over the already harvested kuffar” — infidels — “and continue crushing their remains until it becomes physically impossible to continue by vehicle.”

In the New York attack, the suspect drove over people in the bike lane until he crashed into a school bus.

According to the magazine, the attacker is expected to jump out and use a secondary weapon, like a gun or a knife. The New York attacker did just that: He jumped out with a pellet gun, though he did not appear to have hurt anyone with it. His aim, though, may have also been to use a knife. The complaint states that a black bag containing three knives was found near Saipov after he was shot.

Among the more obscure instructions, however, is the manner in which the assailant is supposed to tell the public of his allegiance to IS. The article states that an assailant should write a note on several sheets of paper, throwing them out the window of the vehicle as the attack is being carried out. The magazine suggests including the phrase, “The Islamic State will remain,” a rendering of the group’s baqiya slogan.

The New York attacker’s papers were found about 10 feet (3m) from the driver’s side of the car, the criminal complaint said.

ADDRESSING THE IS LEADER

On the attacker’s cellphone, recovered at the scene, investigators found several pictures of Abu Bakr Baghdadi, the self-styled caliph of IS.

Recruits learn that before an attack, a pledge of allegiance needs to be recorded. It can be written or recorded as audio or video, but the pledge is supposed to be to addressed to an individual, in this case the caliph of IS, and not to the organisation overall.

This ritual is meant to recreate the way in which early Muslims pledged fealty to the Prophet Muhammad, and later to the caliphs that succeeded him, said Mr Amarnath Amarasingam, a senior research fellow at the Institute for Strategic Dialogue. IS recruits refer to Baghdadi as Emir al-Mumineem, an honorific meaning the commander of the believers, and they will often use a long version of his name — “Abu Bakr Baghdadi Husseini Qurayshi.”

The last term — Qurayshi — is a reference to tribe of the Prophet Muhammad. One of the rules for choosing a caliph is that he must be descended from the lineage of the prophet. Recruits who use this terminology are nodding to this history.

These terms can be heard in the first few sentences of Anis Amri’s pledge of allegiance, released after the Tunisian immigrant used a tractor-trailer to run over shoppers in a Christmas market in Berlin last December, killing 12.

Although Saipov had pictures of Baghdadi on his phone and told investigators that he began plotting his attack after hearing one of the leader’s audio recordings, authorities said, he does not appear to have pledged allegiance in this formal manner. This could reflect someone who was self-radicalised, not coached online, at least not extensively, by IS recruiters.

PROPAGANDA THROUGH CLOSED CHANNELS

At the same time, what the complaint said was found on the attacker’s phone suggests he may have had access to IS’ secret chat rooms on the app Telegram. It is in these chat rooms, known as “channels,” that IS followers congregate and post claims for attacks as well as share videos, including executions.

With numerous lawsuits filed against social media companies by the families of victims of recent IS attacks, the group’s videos are often suspended within hours of being uploaded to YouTube, Twitter or Facebook. The group has increasingly turned to closed channels to share information.

Among the videos that investigators said they found on Saipov’s phone is one of the group’s most disturbing clips, showing the grotesque executions of prisoners forced to wear orange jumpsuits in an echo of the US prison at Guantnamo Bay.

That the suspect was said to have these videos, as well as thousands of images of IS propaganda suggests he may have had access to the group’s Telegram channels.

These channels include online tutorials on how to carry out attacks. For example, the Lone Lions channel routinely posts step-by-step demonstrations showing how to make triacetone triperoxide, or TATP, the explosive compound used in nearly all IS attacks in the West.

More important, these channels serve as digital watering holes, where IS scouts identify potential new attackers.

Numerous attacks in the last three years were carried out by recruits who made contact with IS handlers on the Telegram app, and later migrated to encrypted, one-on-one chats.

Like any other app, Telegram can be deleted from a phone. The complaint does not state if investigators found the app on the two cellphones the suspect left at the scene, or if he erased the digital breadcrumbs leading back to IS. THE NEW YORK TIMES