More than a month later, he was arrested and charged with second-degree felony making threats of terrorism. Since then, he has not seen the outside of the Salt Lake County jail, where he is being held in lieu of a $1 million bail.
Defense attorney Neal Hamilton has long maintained that Stiles made threats he was never able to carry out, that he needs a doctor, not a jail cell.
But the Salt Lake County district attorney's office has not backed off the case.
At a preliminary hearing in June, prosecutors will ask a judge to order the 43-year-old man to stand trial.
Their reasons, a defense motion filed in 3rd District Court this month alleges, are political meant to appease law enforcement and City Creek Center officials.
According to the motion, prosecutors had agreed to enter into a diversion agreement, in which the charge against Stiles would have been dropped in exchange for his entering a mental-health treatment program.
Court documents reveal that Stiles had been put on track to enter mental health court and the criminal case against him would be resolved.
But last month, everything changed.
The case resumed its march toward a preliminary hearing, at which prosecutors would lay out the evidence against Stiles and try to convince a judge there is probable cause to bring him to trial.
If convicted, Stiles could spend up to 15 years in prison.
This was no spontaneous about-face, Hamilton alleged in court documents filed last week.
"In explaining its decision, the State explained it had received communications (including emails) from officers with the Salt Lake City Police Department and from [City Creek's attorneys] regarding the anticipated resolution and dismissal of Mr. Stiles' case," the motion states. "The State clearly represented that it was under pressure to not dismiss this case, and that in light of the publicity a different resolution needed to be reached."
Salt Lake County District Attorney Sim Gill has denied the allegations that his office did anything for any other reason than the pursuit of proper justice.
Gill declined to discuss the particulars of the Stiles case, as the alleged conversations happened under the privacy of plea negotiations.
"We talk about a lot of different things in plea negotiations, but whatever we discuss with defense counsel we don't discuss in the press," Gill told The Tribune on Sunday. "There's no constitutional right to a plea bargain. When we discuss things and look at all the options that we have, ultimately we make our final decision based on that."
Judge Robin Reese will eventually rule on the defense motion, which asks that prosecutors turn over all communications, emails and other exchanges they had with Salt Lake City police and City Creek lawyers.
Hamilton said Sunday he's not sure whether these communications exist or what they contain, but he was told they played a role in the county's decision to continue prosecuting his client.
"We don't have the luxury of wondering if these communications were made. We are required to find out because if they were made, such statements would absolutely be usable at trial," Hamilton said. "Most troubling to me is the representation that there might be some veiled or not so veiled threats that were made to my client."
Stiles has a history of mental illness.
According to charging documents, the day he planned on committing the alleged mass shooting was Sept. 25, which police said was the anniversary of his mother's death.
Stiles does not own a gun. If he tried to purchase one, Hamilton said, "he would be unable to do so."
According to police, Stiles said he had "scoped and mapped out" sites at City Creek Center and at Cinemark Movies 10 in Sugar House. At City Creek, he planned to "just randomly shoot and kill people" at lunch time, police reported.
He then said he planned to go to the Sugar House movie theater at 1 p.m., when it is likely to be less crowded, allowing him to select his targets more carefully, according to police.
Stiles was arrested two days before the alleged attack was to occur after his crisis worker went to the police.
"We understand why people would be troubled or concerned by the allegations in this case so was Mr. Stiles," Hamilton said. "That's why he called 911 and sought police and medical attention. He was uncomfortable with what was going on, but people with mental illness can't always control what they're thinking. They need us to get them help. We should be encouraging this behavior and response not punishing his honesty."
This most recent request for evidence, Hamilton believes, will demonstrate prejudice against his client and unethical practices by the prosecution comes on the tail of another motion he filed asking that the district attorney's office be tossed from the case.
In that filing, defense attorneys accused prosecutor Heather McGinley of going through back-channels to obtain private medical information on Stiles without his consent.
McGinley was assigned to the case about the time the alleged plea deal appeared to unravel.
Gill said the original prosecutor was reassigned to a different part of the office and took over unrelated cases. McGinley's apointment had nothing to do with the Stiles matter in particular, he said.