ISIS has claimed responsibility, without giving evidence, for the deadly terrorist truck rampage in New York City earlier this week, drawing a severe warning from US President Donald Trump who said the group will pay a "big price" for every attack it stages against the United States. The US military has hit ISIS "much harder" over the past two days after the group claimed the attacker was one of their members, Trump said. "They will pay a big price for every attack on us!" Trump wrote on Twitter. The attacker Sayfullo Saipov, 29, was charged in federal court on Wednesday with acting in support of ISIS by plowing the truck down a popular riverside bike trail, killing eight people and injuring a dozen people. According to the complaint filed against him, Saipov told investigators he was inspired by watching the terrorist group’s propaganda videos on his cellphone, felt good about what he had done, and asked for permission to display the organizatoin’s flag in his room at Bellevue Hospital. Saipov was taken to Bellevue after he was shot in the abdomen by a police officer at the time of his arrest. He was allegedly in possession of three knives, thousands of ISIS propaganda images and dozens of videos that showed the group’s militants killing prisoners. The picture of Saipov that has emerged is of a suspect who only radicalized after moving to the United States in 2010. Trump reiterated his call on Thursday for the death penalty against the Uzbek immigrant. Trump had on Wednesday suggested sending Saipov to the Guantanamo Bay military prison in Cuba, where terrorism suspects apprehended overseas are incarcerated, but he said on Thursday doing so would be too complicated. The eight people killed in the rampage were honored by friends and strangers Thursday with a nighttime walk down the riverfront esplanade where the victims died. Some of the marchers carried candles as city lights twinkled on the water. Others pushed bicycles in solidary with the victims, who were cut down on the long bike path that runs the length of Manhattans Hudson River waterfront.