NEW YORK (NYTIMES) - Sayfullo Saipov's arrival in the United States in 2010 began unceremoniously in Ohio.

"My dad introduced him as 'he's new to the United States and he's going to stay with us,'" said Bekhzod Abdusamatov, 22, who recalled Saipov as having arrived from Tashkent, Uzbekistan, knowing little English.

He was a late sleeper who was looking for a job and trying to improve his English, said Abdusamatov, who learnt from a phone notification on Tuesday (Oct 31) that Saipov had been named as the suspect in a terrorist attack in Lower Manhattan.

Witnesses and the authorities said Saipov shouted "Allahu Akbar" or "God is great" in Arabic, as he carried out the attack and left handwritten notes in Arabic next to the truck, said a law enforcement official who spoke under the condition of anonymity because the investigation was ongoing.

Saipov is an Uzbeki national who had a green card, the law enforcement official said. He first entered the country in 2010 through Kennedy International Airport, and apparently remained in the United States after that.

On Tuesday night, law enforcement officials converged on an address in Paterson, New Jersey, believed to be Saipov's home.

Police tape kept onlookers away from Saipov's apartment building near Genessee and Getty avenues. Muslim residents walked by and some lamented that the attack was once again damaging to the image of their religion.

In a phone interview, Kobiljon Matkarov, 37, an Uzbeki immigrant, said he met Saipov in Fort Myers, Florida, several years ago when Saipov was working as a truck driver.

Saipov then moved to New Jersey and began driving for Uber. "He was a very good person when I knew him," Matkarov said. "He liked the US. He seemed very lucky and all the time he was happy and talking like everything is OK. He did not seem like a terrorist, but I did not know him from the inside."

As investigators began on Tuesday to look into Saipov's history, it became clear that he had been on the radar of federal authorities. Three officials said he had come to their attention as a result of an unrelated investigation, but it was not clear whether that was because he was a friend, an associate or a family member of someone under scrutiny or because he had been the focus of an investigation.

Over the last two years, a terrorism investigation by the FBI, the Department of Homeland Security, the New York Police Department and federal prosecutors in Brooklyn resulted in charges against five men from Uzbekistan and one from Kazakhstan of providing material support to the Islamic State in Iraq and Syria (ISIS).

Several of the men have pleaded guilty. It is unclear whether Saipov was connected with that investigation.