This article is more than 2 years old

This article is more than 2 years old

Donald Trump’s decision to call for the death penalty for the suspect in this week’s terrorist attack in New York could threaten his chance of a fair trial, legal experts have warned.

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The president first called for the execution of Sayfullo Saipov on Wednesday and renewed his call on Thursday morning.

“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!” Trump tweeted on Wednesday night.

On Thursday morning he followed up by appearing to rule out sending Saipov to the Guantánamo Bay detention facility in Cuba, something he had mooted on Wednesday.

“Would love to send the NYC terrorist to Guantanamo but statistically that process takes much longer than going through the Federal system,” the president tweeted. “There is also something appropriate about keeping him in the home of the horrible crime he committed. Should move fast. DEATH PENALTY!”

Saipov, 29, has been charged with causing the deaths of eight people and providing material support and resources to a foreign terrorist organization – Islamic State. He is accused of driving the truck down a bike path on Manhattan’s west side, and was hospitalized after being shot by a police officer and arrested.

He told investigators he had been inspired by watching Islamic State videos and began planning Tuesday’s attack a year ago, according to a criminal complaint filed against him on Wednesday.

“Making a broad statement that he deserves the death penalty before he has stood trial is something that absolutely influences jurors – this is coming from the most powerful person in the United States,” said Anna Cominsky, a law professor at New York Law School.

She added: “What happened here was a horrible tragedy, but our constitution says no matter how egregious a crime, a defendant is innocent until proven guilty and in effect the president has already said the person is guilty. It’s very disappointing and it’s not how the system works. I think the legal community is surprised and it’s this particular comment that’s alarming.”

Gannon Coens, a defence attorney at Bodiford Law in Tallahassee, Florida, said Trump was “a very divisive person”.

“If I was defending this client I certainly would not be pleased. It does not help in any way and it would make my job more difficult.”

Coens said the comments might not make it impossible to pick a jury, but would probably slow the process down. The selection process, during which potential jurors are asked if they have heard or seen things that might make them biased in a case, can take weeks or even months in high profile cases.

One legal expert, who asked not to be named, said: “Comments like this could pollute the jury pool. It was inappropriate.”

The judge in the case of army sergeant Bowe Bergdahl, who is waiting to be sentenced for walking off his post in Afghanistan, said recently that his punishment might end up being lighter because of harsh comments made about the soldier by Trump on the campaign trail.

The chances of Saipov receiving the death penalty on federal charges in a court in New York are slim. The last time a federal case tried in New York ended in an execution was 1954. In the most recent case, Ronnell Wilson, who was sentenced to death for murdering two undercover detectives in 2003, had his death sentence overturned based on his reduced mental capacity.

Robert Dunham, executive director of the Death Penalty Information Center, said: “No one is on federal death row in the US for a crime committed in New York state.” There have only been three federal executions since 1963.

Vehicle assaults similar to the New York attack took place in Spain in August and in France and Germany last year, claiming dozens of lives. Saipov told authorities he made a trial run with a rental truck on 22 October to practise turning the vehicle and “stated that he felt good about what he had done” after the attack, the complaint alleged.

The 10-page charging document said Saipov waived his rights to remain silent and avoid self-incrimination in agreeing to speak to investigators without an attorney present from his bed at Bellevue hospital center in Manhattan.

The complaint said Saipov had requested permission to display the Islamic State flag in his hospital room.

Play Video 2:22 Eight people killed after truck drives on to New York bike path – video report

It said he was particularly motivated by seeing a video in which Abu Bakr al-Baghdadi – who led the campaign by Isis to seize territory for a self-proclaimed caliphate within Iraq and Syria – exhorted Muslims in the US and elsewhere to support the group’s cause.

Investigators found thousands of Isis-related propaganda images and videos on a cellphone belonging to Saipov, including video clips showing Isis prisoners being beheaded, run over by a tank and shot in the face, the complaint said.

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US law enforcement officials, speaking anonymously, said Saipov had been in contact with Kadirov and another person of interest in the investigation, though they did not elaborate.

Tuesday’s assault was the deadliest in New York City since 9/11, when suicide hijackers crashed two jetliners into the World Trade Center, killing more than 2,600 people.

Of those killed, five were Argentinian tourists, who were among a group of friends visiting New York to celebrate the 30th anniversary of their high school graduation, one was a Belgian citizen, one was a New York resident and one lived in New Jersey.

Saipov allegedly used a pickup truck rented from a New Jersey Home Depot store to run down pedestrians and cyclists along a 20-block stretch of the bike path beside the Hudson river before slamming into a school bus.

According to authorities, he then left his vehicle shouting “Allahu Akbar” and brandishing what turned out to be a paintball gun and a pellet gun before a police officer shot him in the abdomen.

Saipov, seated in a wheelchair, appeared for a brief hearing in Manhattan federal court on Wednesday evening. Saipov did not ask for bail and was remanded to federal custody. It was not immediately clear where he would be held.

Saipov lived in Paterson, New Jersey, a one-time industrial hub about 25 miles (40km) north-west of lower Manhattan.

On Wednesday there people reacted with terror, disbelief and shock that a neighbor may have perpetrated such an act. But one reaction appeared common: a desire to stay out of the spotlight.

Hilmi, a 56-year-old man who refused to give his last name, said he had seen Saipov once or twice at Omar Mosque, “but he’s not like a member”.

Multiple neighbors confirmed that Saipov had two daughters and a young son, but few were able to describe him beyond that.

Hilmi said he saw Saipov, “take the kids from the van,” but that Saipov had only lived there about six months.

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Saipov lived in an immigrant neighborhood. His immediate neighbors were from Morocco and Macedonia. Workers at the nearby recycling plant are Polish.

The city clearly had jitters. “It’s terrifying,” said Maria Rivas, a 32-year-old mother who lives a few streets from the suspect.

She said she had left work because she was so scared. “It’s really close to home,” she said.

Reuters contributed to this report