Former police officer Derek Chauvin wants a new trial after his conviction for the murder of George Floyd last month, accusing the jury of "misconduct".
The demand comes after a photo emerged of one of the jurors, Brandon Mitchell, wearing a Black Lives Matter T-shirt at a protest in Washington D.C. last August.
The rally included speeches from members of Floyd's family.
The 12-person jury unanimously found Chauvin guilty last month of second degree murder, third degree murder and second degree manslaughter.
The former officer was filmed kneeling on the neck of Floyd, an unarmed African-American man, for nine minutes and 29 seconds, a position he maintained despite Floyd's pleas that he couldn't breathe.
In a fresh court filing today, defence lawyer Eric Nelson said Judge Peter Cahill "abused" his discretion when he refused to move the trial to a different venue. Nelson also asked for a new trial.
Mitchell, 31, attended a demonstration in the American capital on August 28, commemorating the 57th anniversary of the March on Washington, where Dr Martin Luther King jnr made his famous "I Have a Dream" speech.
The photo of him shows him alongside two of his cousins, wearing a T-shirt with King's face and the words: "Get your knee off our necks".
The defence will argue the image is proof that Mitchell was not impartial.
During the jury selection phase of the Chauvin trial, prospective jurors had to answer a 14-page survey gauging their opinions on several topics, including the Black Lives Matter movement.
It included questions about their participation in protests against police brutality.
"Did you, or someone close to you, participate in any of the demonstrations or marches against police brutality that took place in Minneapolis after George Floyd's death?" asked one of the questions.
"Other than what you have already described above, have you, or anyone else close to you, participated in protests about police use of force or police brutality?" asked another.
Mitchell answered "no" to both questions. During jury selection, he also told Nelson that he had a "very favourable" opinion of Black Lives Matter, and that he knew some "great guys" who were police officers.
He said he was capable of being impartial as a juror.
Speaking to the Star Tribute, Mitchell insisted he had been honest throughout the process, and said the march was "100 per cent not" for Floyd specifically.
"I'd never been to D.C.," he said.
"The opportunity to go to D.C., the opportunity to be around thousands of black people. I just thought it was a good opportunity to be a part of something.
"It was directly related to Martin Luther King's March on Washington from the 1960s."
He told WCCO he was at the march to support increasing voter turnout for the 2020 presidential election between Donald Trump and Joe Biden.
"Either way, I was going to D.C. for this event, even if George Floyd was still alive," he said.
Civil rights lawyer Brian Dunn told the Washington Post the photo of Mitchell was "undeniably suggestive of a possible bias in this juror".
Judge Cahill will now have to determine whether Mitchell "lied about, or failed to provide complete answers on whether he has engaged in activism, or whether he has any affiliations with Black Lives Matter that go beyond the mere wearing of the shirt", Dunn added.
"If it is determined that the juror did not provide full disclosure to the defence, the question then becomes whether this lack of candour violated Mr Chauvin's right to a fair trial."
The charges for which Chauvin was convicted come with maximum sentence of 40, 25 and 10 years, respectively.
But Chauvin, who had no previous criminal record, will not be imprisoned for that long. Under Minnesota's sentencing guidelines, the presumptive sentence for both murder charges is 12.5 years, and four years for manslaughter.
The judge is given some discretion to deviate from those guidelines, and in this case the prosecution has indicated it will argue for "aggravating circumstances", which could justify a harsher sentence.
Such circumstances could include Chauvin treating Floyd with particular cruelty and abusing his power as a police officer.