The suspected New York City attacker, Sayfullo Saipov, was interviewed in 2015 by federal agents in the Department of Homeland Security Investigations Unit about possible ties to suspected terrorists, but the agents did not have enough evidence to open a case on him, laws enforcement officials tell ABC News.

Saipov's name and address was listed as a “point of contact” for two different men whose names were entered into the Counterterrorism and Criminal Exploitation Unit’s list after they came to the United States from “threat countries,” one federal official told ABC News.

One of the two men has vanished and is being actively sought by federal agents as a “suspected terrorist.”

Saipov, 29, came to the United States from Uzbekistan through a Diversity Visa Program lottery in 2010, making him a legal permanent resident of the United States upon arrival. He has lived in Ohio, Florida and, most recently, Paterson, N.J., where federal agents interviewed Saipov in 2015.

Authorities say Saipov claimed in a handwritten note found near his truck that he carried out Tuesday’s attack on behalf of ISIS.

Investigators searching Saipov’s online activities have found social media links to people who are or were subjects of terror investigations. However the portrait that is emerging so far is of someone who found ISIS propaganda online with no sense that he was part of a cell or in any way directed to do this.

The vetting process for all visa programs was substantially changed two years after Saipov’s entry to include vetting against a broad array of classified and unclassified information.

The change was prompted by the terror-related arrests in Bowling Green, Kentucky of two individuals who came through an Iraqi refugee program. There was information in Department of Defense files that linked these people to IED attacks against American soldiers in Iraq. At that time, though, the visa vetting process did not include access to that information

ABC News