PATERSON, N.J. – Over the last few weeks, Carlos Batista noticed something odd – his neighbor Sayfullo Saipov would occasionally drive a Home Depot pickup truck on the block, even though he didn't seem to be carrying any building material, or doing any construction work.

Batista, 23, said he noticed Saipov driving the truck around with a couple of his friends.

"They didn't even have one piece of wood in there, and that's why I found it a little suspicious," he said. "And I do construction, so I know when somebody is doing some type of work."

Federal agents suspect the early rentals were part of Saipov's preparation for the attack he carried out Monday – mowing down bicyclists and pedestrians on a busy bike path on the west side of Manhattan.

Eight people were killed and a dozen injured – the deadliest act of terrorism in New York City since the World Trade Center was felled by airplane hijackers in 2001. According to criminal charges filed Tuesday night, Saipov rented the truck on Oct. 22 to practice making turns with the vehicle in preparation for the attack. The criminal complaint said Saipov confessed that he began planning for it about a year ago.

Saipov emigrated to the United States from Uzbekistan in 2010, and before moving to Paterson he lived in Ohio and Florida. Counterterrorism officials say they had not previously investigated him, but his name had surfaced in an FBI probe of a friend, and he was named as a point of contact on immigration paperwork for other immigrants.

Law enforcement officials cautioned that in the small, tightknit world of Uzbek immigrants to the United States, it was not that unusual for Saipov's name to surface in multiple settings. They added that until Monday, federal agents had not found anything to prompt specific concerns about him.

In his confession to authorities after the attack, Saipov left no doubt about his motive – support for Islamic State, also known as ISIS.

According to the criminal complaint filed against him, Saipov "requested to display ISIS's flag in his hospital room and stated that he felt good about what he had done." Investigators also said he had been watching violent Islamic State videos on his phone for months.

Friends and acquaintances said since he came to the United States, Saipov worked intermittently as a truck driver and an Uber driver, but some said he had a bad temper and lost driving jobs because of it.

When his neighbor Batista saw the Home Depot rental truck on his block, Saipov was always driving, and his two friends were passengers. While he found Saipov's use of the truck odd, he didn't stand out in other ways, the neighbor said. Batista thought of him generally as a calming influence in the neighborhood, where he'd lived for about half a year.

One time, when Batista was riding his dirt bike, he got into an argument with two of Saipov's friends. Saipov emerged from his house to break up the dispute. "He was the peacemaker," Batista said. "I went on my way."

Batista did not know the names of the two men Saipov was often seen with.

FBI officials have questioned Saipov's wife, who has denied any knowledge of the planned violence, according to a person familiar with the discussion.

The person, who spoke to his wife by phone Tuesday evening but did not want to be identified, said she seemed "shocked and horrified and scared and sad." At the time, federal agents were at her house, encouraging her to cooperate to ensure no one else was harmed.

Other neighbors on the block of Genessee Avenue where Saipov lived said nothing struck them as unusual about the 29-year-old father of three young children.

Altana Dimitrovska, a tenant who lived in the same small apartment complex, said she was surprised by the news. She used to see Saipov bringing one of his children to school in the mornings. Speaking through a translator, Dimitrovska said she once asked him if he ever went to work, because she would see him on the sidewalk a lot.

"He said, 'Yeah, I do go to work.' But I never saw him going to work," she said. Asked if she ever saw anything suspicious about the man, the 63-year-old neighbor replied, "No, no, no."

Before he lived in Paterson, Saipov and his family lived in an apartment in Tampa, next to Kyong Eagan. Eagan called Saipov "shy, soft-spoken, very quiet."

"He was a small guy, only 100 pounds and 5 feet tall," she said. "I could have punched and knocked him down. I can't believe this small guy did this monstrous thing."

During the time Saipov and his family were her neighbors, she said, he was very generous to her.

"He would give me a whole case of water from his truck," Eagan said. "Sometimes he would give me a whole box of mango juice and never charged me." Eagan said he also brought her home-cooked meals and said he wanted to share food from his country with her.

Eagan said that on most weekends, about 30 men – young and old – gathered at Saipov's house to pray.

"I just have to pinch myself over and over," Eagan said. "That's my neighbor. That's my neighbor. This doesn't make sense to me. He was a very polite man. He offered me food and drinks. He never said anything hateful about the country. He's a monster now."

Eagan says Saipov lived in her apartment complex just over a year and left Tampa this past spring. He said he left her a vacuum cleaner, brooms, a mop, two printers and a computer, and on March 8, according to her receipt, she donated them to the Salvation Army.

"He was in a big hurry to move out of there," Eagan said.

In Ohio, where Saipov lived when he first immigrated to the United States, one of his friends described a darker personality – one prone to fights and misunderstandings.

"Everyone in our neighborhood knew he was a little bit troubled," said Mirrakhmat Muminov, a 38-year-old truck driver living outside Akron, Ohio. He remembered Saipov once parked in a handicapped spot and that someone tried to make him move his car.

"He started yelling, 'Is that your place? Are you buying this place? Why are you telling me where to park?' " Muminov said. "This aggressive behavior happened all the time."

On the job, sometimes customers would get mad if he was late for a delivery and refuse to pay him.

"He would raise his voice and say, 'How can you not pay me?' " Muminov said. "The customers would call us to report the problem. We would warn him a couple times, 'You have to be nice to customers.' And then we fired him."

Muminov said that Saipov lived in the Cuyahoga Falls area, which has an Uzbek immigrant community of several dozen refugees, for about three years. Saipov went to the neighborhood mosque but was not an active member and was not involved in community activities.

Abigail Hauslohner, Jon Silman, Julie Tate and Katie Mettler of the Washington Post contributed to this article.