The complaint also said Saipov had requested permission to display Islamic State's flag in his hospital room and said he felt good about what he had done. Photograph:( Reuters )
The Uzbek immigrant behind New York's worst attack in 16 years confessed to acting in the name of the Islamic State group and "felt good" about the killings, having planned an assault for a year, investigators said Wednesday.
The shocking details emerged as federal prosecutors filed terrorism charges against Sayfullo Saipov, who subsequently appeared in court in a wheelchair -- he had been shot in the abdomen by police -- 24 hours after mowing down pedestrians and cyclists, and colliding with a school bus.
US President Donald Trump vowed an immediate crackdown on the visa program that he said allowed the 29-year-old to immigrate in 2010, saying he would "certainly consider" sending the suspect to the military detention center at Guantanamo Bay.
The attack killed eight people, five of them childhood friends from Argentina celebrating 30 years since their high school graduation, a 31-year-old Belgian mother, and two US men, from New York and neighboring New Jersey.
Of 12 wounded, four remained in critical condition following the deadliest attack in America's financial capital since the Al-Qaeda hijackings on September 11, 2001.
Saipov first started planning an attack a year ago, before settling two months ago on using a truck to kill as many people as possible during Halloween celebrations, according to a federal terrorism complaint.
Prosecutors unveiled the charges, saying he had waived his rights and confessed to being inspired by IS propaganda, after yelling "Allahu Akbar" ("God is Greatest" in Arabic) upon exiting a rented pickup truck in Lower Manhattan on Tuesday.
"Saipov committed this attack in support of ISIS," US acting Manhattan attorney Joon Kim announced.
Saipov appeared in a wheelchair before a US magistrate in Manhattan federal court, where the charges were formally read.
He was not required to enter a plea and was afterward sent to a federal detention facility, most likely in New York, a spokesman for the US Attorney's office told AFP.
He was found in possession of multiple knives in a black bag, a Florida driving license and two cell phones that contained thousands of IS propaganda images and dozens of IS propaganda videos, Kim said.
The files depicted "among other things, ISIS fighters killing prisoners by running over them with a tank, beheading them, and shooting them in the face," Kim added.