On the day of his arrest, Shurtleff used the DOJ's decision as a shield, arguing the state charges against him were trumped up for political purposes.
"The Department of Justice's agenda must not have been political," Shurtleff said, "because, believe me, the resources of the federal government in investigating and prosecuting crime far exceed that of any county prosecutor in the state of Utah."
So which is it? Were DOJ prosecutors the adults in the room, who passed on a flawed investigation, or did they bungle a serious political corruption case involving the state's former top cops?
Don't expect the DOJ to offer any insights. The department declined to comment on the arrests of Swallow and Shurtleff or on its decision to bow out of the case.
That response frustrated Scott Burns, former executive director of the National District Attorneys Association who once worked as Iron County's top prosecutor.
"We are entitled to an answer," he said. Burns said it is "highly unusual" for the FBI to continue pursuing a criminal case with local officials after the DOJ declines to prosecute.
"Which tells me," he said, "the law enforcement arm of the Department of Justice truly believed these crimes occurred and it was unacceptable conduct."
Noting he is not involved in this case, Burns said the evidence presented is "tailor made for a federal RICO case," the racketeering law often used to prosecute the mob and street gangs.
Shurtleff and Swallow were charged with "a pattern of unlawful activity," the Utah equivalent of that federal law.
Salt Lake County District Attorney Sim Gill announced the charges at a news conference held at the FBI office in Salt Lake City. Gill praised the FBI for continuing to work on the case and scolded the DOJ's Public Integrity Section for backing away last September.
"I'd be less than honest with you if I didn't say to you I have been very disappointed with what the DOJ did or didn't do," Gill said. "Really this case is not something we should be prosecuting as local prosecutors."
Mary Rook, special agent in charge of the FBI's Salt Lake City office, said the bureau's job is the "pursuit of justice," using whatever avenues are available.
"The investigation of public corruption is one of the highest priorities of the FBI," she said. "Left unchecked, corruption can erode the public trust of the citizens in their government and undermine those institutions which exist to serve the public."
The investigation was led by Gill, a Democrat, and Davis County Attorney Troy Rawlings, a Republican, with help from the FBI and the state Department of Public Safety. Benefiting the criminal probe were previous investigations by the lieutenant governor's office into election irregularities and by the Utah House into possible impeachment before Swallow stepped down.
"We took this very seriously even when the feds did not," Lt. Gov. Spencer Cox said, "and we are grateful we were able to work toward restoring that public trust."
Utah Senate President Wayne Niederhauser said the House investigation was based in part on the DOJ's actions.
"We feel like the feds were dropping the ball," said the Sandy Republican.
Kelly Patterson, a political scientist at Brigham Young University, said there are plausible reasons why DOJ would pass on this case. "They have literally hundreds, if not thousands, of cases that they're culling through trying to figure out which ones they're going to spend their resources on," he said, "and in the benefit-cost analysis what's the probability of them getting a conviction."
That's the point Shurtleff made at his news conference.
"I had hoped that Mr. Gill would do the right thing, like the U.S. Department of Justice did, and not abuse his power and position of district attorney to bring charges he knows he cannot possibly prove beyond a reasonable doubt."
The truth of Shurtleff's statement will be tested as the case against him unfolds, but unless the DOJ decides to break its silence, why federal prosecutors punted will likely remain a mystery.
Dan Harrie contributed to this report.