NEW YORK - The suspect in the terror attack in New York that left eight people dead and another 12 injured left a note that referenced the Islamic State of Iraq and Syria (ISIS), a federal law enforcement source confirmed to CBS News.

CBS News has learned Sayfullo Habibullaevic Saipov, 29, is the suspect in the attack, which New York City officials describe as an act of terror.

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Sources tell CBS News' senior investigative producer Pat Milton that Saipov yelled, "Allahu Akbar" -- Arabic for "God is great" -- when he exited a rented Home Depot pickup truck after hitting pedestrians.

CBS News national security analyst Fran Townsend says there was an extremist group there, called the Islamic Movement of Uzbekistan, which pledged allegiance in 2015 to ISIS after about seven years of al Qaeda affiliation. Both al Qaeda and ISIS have urged followers to carry out vehicle attacks.  

According to Townsend, investigators will be looking into whether he was motivated by IMU or other extremist groups and if he had any contact with him -- which is one reason they will be searching Saipov's electronic devices.   

New York Governor Andrew Cuomo said the attack appeared to be a "lone wolf" incident with no apparent link to a wider terrorist plot.  
Saipov doesn't appear to have an extensive criminal background, CBS News' justice and homeland security correspondent Jeff Pegues reports. Both the FBI and the NYPD are "digging" into Saipov's background, Pegues reports.

NYPD Commissioner Joseph O'Neill said Saipov drove onto a bicycle path at Houston and West Street at 3:05 p.m. local time. The suspect struck several pedestrians and cyclists before colliding with a school bus at Chambers St., O'Neill said. After exiting the vehicle and yelling, he was shot by police and taken into custody.

Cuomo, O'Neill and de Blasio praised the work of an officer, identified by CBS New York as 1st Precinct Officer Ryan Nash, a five-year NYPD veteran, who they said stopped the assailant before more people were hurt.

CBS New York said Nash was taken to the Bellvue hospital for ringing in his ears following the shooting. He is a native of Long Island.

The Associated Press contributed to this report.