Federal prosecutors said Wednesday that Sayfullo Saipov was "consumed by hate and a twisted ideology" when he ran down dozens of people on a New York City bike path, killing eight people and injuring 12 others.
Saipov, 29, was charged with providing material support to a terrorist group and committing violence and destruction of motor vehicles in Tuesday's attack, in which he drove a rented Home Depot truck down the path near the World Trade Center site.
Law enforcement officials described the initial charges as "holding charges," meaning that more are expected to be filed.
Saipov nodded his head repeatedly as he was read his rights in a brief court proceeding that he followed through a Russian interpreter. Judge Barbara Moses set his next court date for Nov. 15.
His court-appointed lawyer, David Patton, said Saipov was in "a significant amount of pain" and asked that he get wound care and a wheelchair or crutches in the federal lockup where he's being held without bail.
Outside of court, Patton called for fair treatment of his client.
"I hope, given all of the attention in this case and all of the attention that it's sure to continue to receive, that everyone lets the judicial process play out," he said. "I promise you that how we treat Mr. Saipov in this judicial process will say a lot more about us than it will say about him."
Prosecutors said Saipov had 90 videos and 3,800 photos on one of his two cellphones, many of them ISIS-related pieces of propaganda, including images of prisoners being beheaded, shot or run over by a tank.
Saipov left behind knives and a note, in Arabic and English, that included Islamic religious references and said, "Islamic Supplication. It will endure," FBI agent Amber Tyree said in court papers. "It will endure" commonly refers to ISIS, Tyree said.
Questioned in his hospital bed, Saipov said he had been inspired by ISIS videos that he watched on his cellphone and began plotting an attack about a year ago, deciding to use a truck about two months ago, Tyree said.
During the last few weeks, Saipov searched the internet for information on Halloween in New York City and for truck rentals, the agent said. Saipov even rented a truck on Oct. 22 to practice making turns, and he initially hoped to get from the bike path across lower Manhattan to hit more pedestrians on the Brooklyn Bridge, Tyree said.
He even considered displaying ISIS flags on the truck during the attack but decided against it because he did not want to draw attention, authorities said.
John Miller, deputy New York police commissioner for intelligence, said Saipov "appears to have followed, almost exactly to a T, the instructions that ISIS has put out."
In the past few years, the ISIS has exhorted followers online to use vehicles, knives or other close-at-hand means of killing people in their home countries. England, France and Germany have all seen deadly vehicle attacks since mid-2016.
A November 2016 issue of the group's online magazine detailed features that an attack truck or van should have, suggested renting such a vehicle, and recommended targeting crowded streets and outdoor gatherings, according to the SITE Intelligence Group, a militant-monitoring agency.
Carlos Batista, a neighbor of Saipov's in Paterson, N.J., said he had seen the suspect and two friends using the same model of rented truck several times in the past three weeks.
It was not clear whether Saipov had been on authorities' radar. Miller said Saipov had never been the subject of a criminal investigation but appears to have links to people who have been investigated.
In Tuesday's attack, Saipov drove his speeding truck for nearly a mile along a bike path, running down cyclists and pedestrians, then crashed into a school bus, authorities said. He was shot in the abdomen after he jumped out of the vehicle brandishing two air guns, one in each hand, and yelling "Allahu Akbar."
The attack killed five people from Argentina, one from Belgium and two Americans, authorities said. Of the 12 who were injured, nine remained hospitalized in serious or critical condition.
Saipov lived in Ohio and Florida before moving to New Jersey around June, authorities said.
Birth records show he and his wife had two daughters in Ohio, and a neighbor in New Jersey said they recently had a baby boy.
Saipov was a commercial truck driver in Ohio. More recently, he was an Uber driver.
In Ohio, Saipov was an argumentative young man whose career was falling apart and who was "not happy with his life," said Mirrakhmat Muminov, a fellow truck driver from heavily Muslim Uzbekistan.
"He had the habit of disagreeing with everybody," Muminov said.
He said he and Saipov would sometimes argue about politics and world affairs, including Israel and Palestine. He said Saipov never spoke about ISIS, but he could tell his friend held radical views.
Fox News' Catherine Herridge and Jake Gibson contributed to this report. The Associated Press also contributed to this report.