Sayfullo Saipov, the man accused of killing eight people by mowing down pedestrians and cyclists on a Manhattan bike path, plotted for weeks and then carried out the attack in the name of the Islamic State (ISIS), officials said Wednesday.

Saipov is a legal permanent resident of the United States who arrived from Uzbekistan in 2010 through a diversity visa program. Officials said Saipov was influenced by ISIS after coming to the United States. He left notes pledging his allegiance to the group, authorities said, though more direct connections between Saipov and ISIS have not been identified.

The notes were handwritten in Arabic, and essentially said that the Islamic State would endure forever, according to John Miller, deputy New York police commissioner for intelligence and counterterrorism, who spoke to reporters at a briefing on Wednesday. ISIS has urged its followers to use vehicles to carry out attacks.

"He did this in the name of ISIS," Miller said. "He appears to have followed almost exactly to a T the instructions that ISIS has put out in its social media channels before with instructions to their followers on how to carry out such an attack."

The new details came as authorities continued to explore the violent rampage that tore through a stretch of Lower Manhattan and became New York's deadliest terrorist attack since Sept. 11, 2001.

Police say Saipov climbed into a rental truck on Tuesday afternoon and careened down a bike path along the Hudson River, slamming into numerous people before he was wounded by police and taken into custody. He drove southbound on the path "at a high rate of speed" and appeared to specifically target cyclists and pedestrians, Miller said.