Miller cited a "political controversy" in rejecting the case against Tom Gallegos.
But Attorney General Mark Shurtleff has agreed to screen the case, said his spokesman, Paul Murphy.
"Involving the Salt Lake County District Attorney's Office in a political controversy within Salt Lake City is not a prudent use of this office's resources," Miller wrote to City Attorney Ed Rutan.
Gallegos sent graphic photographs over a work e-mail account to a police sergeant between February 2005 and October 2006, according to police records. That's a potential third-degree felony under Utah law.
Gallegos was also accused of sending sexually explicit e-mails twice during the same period.
The Police Department issued a written reprimand to Gallegos for the e-mails in January. But Mayor Rocky Anderson caught wind of the e-mails last month and asked for further investigation.
City prosecutor Sim Gill normally prosecutes city employees accused of breaking laws but declined to look at the case because of a conflict of interest. Gill said Gallegos has worked closely with prosecutors in his office.
Because of the conflict, Rutan asked Miller to review the case.
In her denial to look at the case, Miller said it had been pending for almost two years and the city had already taken action against Gallegos.
"The city did not seem to find any impropriety in being involved at the time," Miller said.
The Salt Lake City Police Civilian Review Board, an independent body, disagreed with the department's written reprimand, saying the department should have punished Gallegos for insubordination as well.
Gallegos received another written reprimand in January for sexual harassment for a comment he made to a female co-worker.
In February 2006, Gallegos was asked to sign a copy of the department's policy on personal contacts after sending an inappropriate text message to a co-worker. The review board disagreed with this decision, suggesting punishment for conduct unbecoming of an officer.
Gill, who lost to Miller in the D.A.'s race last fall, said he was surprised by Miller's response.
"When you take the job of district attorney, you have to make tough decisions," Gill said. "But you don't shy away from making a decision that's your responsibility because there might be some political issues."
Former Salt Lake County District Attorney David Yocom said Miller's response was unusual.
"In my entire 42 years as a lawyer in Salt Lake County, I've never heard of that as a reason for not screening a case," Yocom said. "Either the evidence is there or it's not."
Miller rankled Yocom when she took over in January by dropping a felony assault charge against a Granite School District police officer who shot and wounded an unarmed man during a foot chase in October 2004.
In that case, Miller said she did not have enough evidence to prove the officer did not act in self-defense.
Last month, Miller declined to file charges against two Salt Lake County deputies in the Jan. 16 shooting of Joseph Blair, despite her investigators' findings that the use of deadly force was unjustified.