NEW YORK (WASHINGTON POST) - Investigators in Uzbekistan combed through records and intelligence reports on militant factions in the Central Asian nation on Wednesday (Nov 1), seeking to fill out the portrait of a 29-year-old immigrant who brought Halloween death and bloodshed to a Manhattan bike path.

The Uzbek probe came as US officials also dug deeper into the life of the suspect, identified as Sayfullo Saipov, since he arrived in the United States six years ago and shifted from New Jersey to Ohio and Florida.

Saipov was wounded by police as they surrounded the rented flatbed truck on Tuesday after it mowed through cyclists and others on the popular bike route overlooking the Hudson River.

At least eight people were killed and 11 were injured along a path of strewn bodies and cast-off items - purses, backpacks, shoes - similar to scenes in other attacks in Berlin, London, Barcelona and elsewhere where vehicles have been uses as tools of terrorism.

Five Argentines and a Belgian were among the victims in New York.

According to a video from the scene, the attacker jumped out of the wrecked vehicle brandishing what appeared to be handguns.

Some witnesses said he shouted "Allahu Akbar", meaning "God is great" in Arabic.

Inside the rental truck, investigators found a handwritten note in which Saipov had declared his allegiance to the Islamic State in Iraq and Syria (ISIS), according to officials.

Among the chief questions for investigators waiting to interrogate Saipov is whether he acted alone or had possible connections to wider militant cells.

US law enforcement officials identified Saipov as an immigrant from Uzbekistan, but officials in the country said they were trying to confirm details on the suspect, including his background.

Still, the Uzbek connection has emerged as a central element in the investigation. A message to President Donald Trump from Mr Shavkat Mirziyoyev, the President of Uzbekistan, promised to use all resources to help in the probe.

Shorty after the attack, Mr Trump made a reference to ISIS in a Twitter post, saying: "We must not allow ISIS to return, or enter, our country after defeating them in the Middle East and elsewhere. Enough!

But it was unclear whether Saipov had possible deeper connections to the group or was a so-called "lone wolf" influenced by militant ideology.

Uzbekistan also has homegrown factions that have allied with larger militant groups. Uzbek militants have long fought in Afghanistan, where they were allied with the Taleban, and they have launched attacks on US and Nato troops.

In 2015, a faction of the Islamic Movement of Uzbekistan, which has a strong presence in Afghanistan, pledged allegiance to ISIS.

An Uzbek gunman carried out a New Year's day shooting rampage in Istanbul that left 39 people dead. Turkish authorities said the attacker was linked to an ISIS-inspired group and received training in Afghanistan.

Before dawn in New York, the bike path remained blocked off by police tape between Houston and Chambers streets.

Dozens of police officers guarded the perimeter while crime scene investigators wearing white suits slowly searched the length of the path.

Police closed streets on Wednesday (Nov 1) around the area near the West Side Highway.

The attack could intensify the political debate over immigration and security. Mr Trump has argued for much tougher screening of immigrants to prevent terrorism, and opponents of those policies have sought to block his efforts in the courts.

Uzbekistan was not among the countries named in any version of the President's travel ban, which largely targeted a number of majority-Muslim countries.

Mr Trump said on Tuesday he was tightening immigrant screening, tweeting: "I have just ordered Homeland Security to step up our already Extreme Vetting Programme. Being politically correct is fine, but not for this!"

Saipov had been living in Paterson, New Jersey, before the attack, and rented the vehicle in that state before driving it into Manhattan, officials said.

The violence was terrifyingly similar to vehicle attacks carried out in Europe, where ISIS supporters have used cars and trucks to strike pedestrians in crowded streets, a tactic that has been employed in France, Britain, Germany, Sweden and Spain.

"This certainly bears all the hallmarks of an ISIS-inspired or Al-Qaeda-inspired attack," said Representative Adam B. Schiff of California, the ranking Democrat on the House Intelligence Committee, whom the FBI briefed on the attack on Tuesday evening.

"We have to expect that as the capital of the caliphate has now fallen, there are going to be increasing efforts to show that they remain dangerous and lethal, and to expand the virtual caliphate. But at this point, we don't know whether this was an ISIS-directed attack or merely someone acting out of radical inspiration."

An officer from the 1st Precinct approached Saipov and shot him in the abdomen after the attacker crashed the rented Home Depot flatbed truck into a school bus, police said.

He was taken to a hospital, but officials did not discuss his condition or location. The weapons he was brandishing turned out to be a pellet gun and a paintball gun, police said.

"This is a very painful day in our city," said New York Mayor Bill de Blasio. "Based on the information we have at this moment, this was an act of terror, a particularly cowardly act of terror aimed at innocent civilians."

Saipov moved to the United States from Uzbekistan about six years ago, said Ms Dilnoza Abdusamatova, 24, who said Saipov stayed with her family in Cincinnati for his first two weeks in the country because their fathers were friends. Some officials said he arrived in 2010.

Ms Abdusamatova said Saipov then moved to Florida to start a trucking company. Her family members think he got married about a year after arriving in the United States and may now have two children.

Around that time, she said, he cut off contact with them. "He stopped talking to us when he got married," Ms Abdusamatova said.

Saipov had lived in an apartment complex, Heritage at Tampa, near the Hillsborough River.

On Tuesday evening, two plainclothes investigators were seen departing the community, having interviewed several residents and others in the surrounding neighbourhood. The investigators declined to answer any questions.

"Four FBI agents came and told me he used to live here," said Ms Venessa Jones, who said she lives in an apartment above the one Saipov rented. Neighbours at the complex said they didn't know Saipov.

At the bike path, two men holding coffee cups approach the police tape early on Wednesday.

"I don't see what happened," one said.

"You don't know what happened? Yesterday. Someone drive a truck into people," the other said.

"Did people die?"

"Yeah," said the man. "People died."