Judge Leslie Ghiz barred the prosecution from presenting the T-shirt as evidence, saying it was "far too prejudicial" to be allowed. The black T-shirt has the words "Great Smoky Mountains Tennessee" and "1934," the national park's founding year, surrounding the Confederate flag.
"It doesn't matter if the shirt said 'God loves all his children,'" Ghiz said at the time. "I wouldn't allow that either."
The flag is viewed by many as a symbol of slavery and oppression; to others, it's a symbol of Southern pride. Tensing, who is white, said at his first trial the T-shirt had "no meaning" to him. DuBose was black.
Jurors are supposed to only consider and deliberate over evidence a judge allows. Still, Mathews said he learned it was discussed in the jury room during deliberations at Tensing's second trial -- in spite of Ghiz's ruling. He spoke with four jurors and one alternate, he said.
"Had the jury found him guilty of something, he might have had something," former judge Norbert Nadel said. But, he added, it's irrelevant now that Deters has dropped the case.
The shirt became widely known in the two years since Tensing killed DuBose. The fact jurors discussed it doesn't necessarily mean the trial should have been moved, Nadel said. Judge Megan Shanahan allowed jurors to hear about the shirt during the first trial last November.
Tensing was a police officer for the University of Cincinnati when shot DuBose in the head during a traffic stop in the city's Mount Auburn neighborhood two years ago. He claimed DuBose tried to drive off from the stop, and that he feared for life because his arm was caught in the car.
The trials centered on whether Tensing truly was in danger and if his actions were appropriate.
Mathews said Tensing is "relieved" Deters dropped the case, "but he's very concerned that it's been referred to the Department of Justice."
Deters said the Justice Department has asked to review the case for potential civil rights violations, and his office has turned over all his case files to the U.S. Attorney's office. But he also cautioned the federal government works slowly.
"I don't believe there's any bit of evidence that would substantiate a federal civil rights violation," Mathews said.
He also said Tensing and his family are concerned about mounting legal costs as the federal government now takes up the case. For now, Tensing is working at his father's company.