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The U.S. justice system works too slowly, President Donald Trump said in an interview that aired Thursday night, urging swift punishment for the man charged with killing eight people with a rented truck in New York.

In an interview with Fox News' Laura Ingraham, which the network said was taped ahead of time, Trump called Sayfullo Habibullaevic Saipov an "animal." In a promotional clip that Fox released earlier in the day, Trump complained that Saipov would be "tied up forever in the court system."

President Donald Trump at the White House on Wednesday. Evan Vucci / AP

Saipov, 29, has been charged with but not convicted of providing material support to a terrorist organization and using a vehicle in a destructive, violent act in Tuesday's deadly attack in lower Manhattan.

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As president, Trump oversees the Justice Department, which would be responsible for bringing Saipov to trial. The remarks echoed the president's statements and tweets since Tuesday making it clear that he believes that Saipov is guilty and should be executed.

NYC terrorist was happy as he asked to hang ISIS flag in his hospital room. He killed 8 people, badly injured 12. SHOULD GET DEATH PENALTY! — Donald J. Trump (@realDonaldTrump) November 2, 2017

"You look at some of the cases that are going on forever, and you have them dead to rights," Trump told Fox News in the clip that was published earlier. "No, the justice system has to go quicker. And it has to be, really, stronger and fairer."

Trump told reporters Wednesday that he would "certainly consider" sending Saipov to the U.S. detention facility at Guantánamo Bay, Cuba, a decision that an administration official told NBC News that Trump likely has no legal authority to make.

Trump is scheduled to depart on Friday on a five-country, 10-day tour of Asia designed to strengthen diplomatic and economic partnerships while contending with North Korea's nuclear threat.

"I must tell you, North Korea's a thing that I think we will solve, and if we don’t solve it, it's not going to be very pleasant for them. It's not going to be very pleasant for anybody."

On other topics, the president: