When President Trump tweeted that he thinks New York City attack suspect Sayfullo Saipov should get the death penalty, he may have inadvertently made it more difficult for the prosecutors on the case.

The issue is with the lawyers’ ability to find an unbiased group of jurors, now that the most-followed world leader on Twitter has weighed in.

“Comments by senior government officials can unduly influence a jury pool and their views from otherwise reaching a fair and just verdict,” explains Mark Zaid, who has a legal practice focused on national security law. “In this case, President Trump’s statements have already clearly had an impact. Not only did he assert guilt but he also imposed sentence.”

This could create delays and headaches for the lawyers as they try to select jurors from New York who haven’t been swayed by the president’s statements or any of the pretrial publicity.

“Everyone in the system, the prosecutors, the defense attorneys, and the judge are going to have to spend time trying to account for [Trump’s] statements and trying to reduce the effects of them to ensure the defendant has a fair trial,” says Renato Mariotti, a former federal prosecutor.

Presidents and other powerful government officials are generally advised not to comment on pending criminal cases for this reason. The most likely effect of Trump’s public prejudging of the case will be enhanced scrutiny during jury selection, with more extensive questions for the jurors and instructions from the judge about what they may have heard about the case.

In a more extreme scenario, the defense could ask to move the venue of the trial. But experts say that when the pretrial publicity causing problems comes from the President of the United States, changing the location probably wouldn’t help much.

“The reason comments from presidents are particularly prejudicial is they are given national dissemination, so it’s often very difficult to find someone who is unaware of presidential comments,” says Jonathan Turley, professor at George Washington University Law School. “And you don’t want to whittle a jury pool down to those people effectively living in a cave.”

This isn’t the first time that Trump has publicly advocated for the death penalty in a high-profile trial. In 1989, when Trump was a private citizen, he ran an ad in the New York Daily News saying the “Central Park Five” — a group of five black and Latino teenagers who were charged with beating and raping a jogger – should be executed if the victim died.

“I want to hate these muggers and murderers,” Trump wrote, the Daily News recounts. “They should be forced to suffer and, when they kill, they should be executed for their crimes.”

The five suspects confessed to the crime on videotape and were convicted, but were then exonerated by DNA evidence years later. Still, despite the DNA evidence clearing them and their claims that the confessions were coerced, Trump remains convinced of their guilt.

As a presidential candidate in 2016, Trump said, “They admitted they were guilty. The police doing the original investigation say they were guilty. The fact that that case was settled with so much evidence against them is outrageous. And the woman, so badly injured, will never be the same.”

Saipov, who is accused of killing eight people in a truck attack in Manhattan on Halloween, will face terrorism charges.

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Write to Tessa Berenson at tessa.berenson@time.com.