The man arrested after Tuesday’s terror attack in New York had been planning the attack for weeks “in the name of ISIS,” according to information released Wednesday by police officials. The man, who authorities had said they suspected was radicalized in the U.S., also appeared to have connections with people who have been the subjects of terrorism investigations.

Police officials also said they discovered the suspect had been on the radar of federal terrorism investigators, the New York Times reports.

Sayfullo Saipov, a 29-year-old immigrant from Uzbekistan who came to the U.S. in 2010, is accused of driving a rented pickup truck onto a crowded Manhattan sidewalk around 3 p.m. Tuesday, killing at least eight people. The Times and other sources reported he shouted “Allahu akbar” as he left his truck. He was shot in the abdomen by a police officer. He underwent surgery and remained in the hospital.

Handwritten notes from the driver at the scene said in Arabic “The Islamic State will endure forever,” authorities said, but ISIS has not yet claimed the attack. In a series of tweets, Rukmini Callimachi, the correspondent for the Times covering ISIS, said the phrase is an ISIS slogan. “I can’t overstate how closely tied the phrase “The Islamic State remains” / “The Islamic State endures forever” is with the terror group,” she wrote in a tweet.

“Last year in their magazine issue focusing on vehicular attacks, ISIS instructed their followers to use a truck to crush people,” she wrote. “Less well-known is that same issue instructed the attacker to leave notes at the scene which make his allegiance to ISIS known.”

In an interview with the Associated Press, an Ohio truck driver, who knew the suspect because they were both Uzbek truck drivers, said Saipov was an angry, argumentative man “not happy with his life” who lost his insurance because of traffic tickets and whose truck engine blew up a few months ago.

A preacher at a mosque in Tampa, Florida, told the Times he had tried to steer Saipov from radicalism and remembered him as someone who was at times explosively angry. He would get “emotional over issues related to the Muslim community,” the Times reported. He was “devoted to outward observances of Islam, like his beard, but not necessarily the substance.” In Florida, where he moved to in 2015, he struggled to find work, according to the preacher.

He moved to New Jersey in March to be closer to his wife’s family, the preacher told the Times. The couple had their third child in the summer, he said.

Saipov is a legal permanent resident who entered the country through the Diversity Visa Lottery Program, according to the U.S. Department of Homeland Security. Trump, who on Twitter called the program a “Chuck Schumer beauty,” called on Congress to eliminate the program, according to the AP.