NEW YORK -- From his hospital bed, Sayfullo Saipov proudly told investigators how he had rented a truck and used it to fatally run down cyclists and pedestrians on a New York City bike path, all in the name of the Islamic State.
He assured them he acted alone. U.S. counterterrorism agents want to make sure.
Since the attack that killed eight people, the New York Police Department and the FBI have been working behind the scenes to study his past, question his family and friends, examine his cellphone and online activity and hunt for any clues that might identify others plotting similar attacks.
That search has already revealed instances where Saipov had contact with other people who had drawn law enforcement scrutiny.
"What we are looking for is how has he touched the subjects of other investigations, what is his connectivity to those people," said John Miller, the NYPD's top counterterrorism official.
Saipov, 29, came to the U.S. legally in 2010 from Uzbekistan, where officials say he had no history of trouble with the law. He first lived in Ohio, where he was a commercial truck driver, then Florida. He most recently lived in New Jersey with his wife and children and worked as an Uber driver.
Since Saipov's arrest, investigators have tried to determine if he had interactions with any other terror suspects, including four Uzbeks charged in separate case in Brooklyn with conspiring to support the Islamic State group. Prosecutors have accused them of seeking to travel to Pakistan to fight for the group.
The FBI has also learned that Saipov was at a wedding two years ago that was also attended by another immigrant from Uzbekistan who was -- and remains -- under investigation.
Agents have also interviewed many people who knew Saipov, including a friend who was questioned for hours over several days. So far, that man, a fellow immigrant from Uzbekistan, is only considered to be a witness, according to two law enforcement officials.
Investigators have interviewed Saipov's wife, who was cooperative but provided no clues, and visited a mosque in New Jersey, where the defendant was living, said one of the officials. Both officials weren't authorized to detail the probe and spoke on condition of anonymity.