But roughly a year later, a federal grand jury indicted the man on charges that he intentionally killed a law enforcement officer and committed other crimes leading up to and related to the shooting of Fox in January 2010.
In a motion filed Tuesday, Roman's attorneys argue that their client has either been convicted or acquitted in district court of all of the federal court charges and should not be facing them again.
"Little did Mr. Roman or any of the jurors know that the [Aug. 17] proceedings during which the rest of Roman's life was at stake would be more properly characterized as a trial run than a jury trial," defense attorney Jeremy Delicino wrote in the motion.
When the 11-count indictment was returned in September, David Barlow, U.S. Attorney for Utah, said filing federal charges was not a do-over of the district court trial, but rather was an indication that federal interests were not resolved in state court proceedings against Roman.
"The state government and federal government are always free to pursue their own prosecutions," he said during a news conference.
Roman's attorneys said in their motion that federal prosecutors are relying on the "dual sovereignty exception" to the Fifth Amendment's Double Jeopardy Clause. They argue that this exception is highly criticized by legal experts and is unconstitutional.
"The comfort provided by the finality of a verdict is purely illusory if the dual sovereignty exception permits one governmental entity to ignore the outcome of a trial by another," the motion reads.
Roman allegedly initially confessed to killing Fox after she pulled over his vehicle around 1 a.m. on Jan. 5, 2010. He later recanted and, during his state court trial, claimed another man the deputy's brother shot Fox with an AK-47. Deputies had been tailing the two for several hours as part of a drug investigation.
Fox's brother, Ryan Greathouse, committed suicide in 2010 and never testified in the case.
A 4th District Court jury acquitted Roman of the aggravated murder charge for allegedly killing Fox, but found him guilty of two lesser third-degree felonies tampering with evidence and possession of a firearm by a restricted person. He was sentenced in October 2012 to two consecutive zero-to-five-year prison terms.
Roman has pleaded not guilty to federal charges, which include one count of killing a law enforcement officer while fleeing apprehension on a drug violation, one count of using a firearm in relation to a crime of violence (killing Fox), three counts of distribution of methamphetamine, three counts of possession of a firearm while drug trafficking, one count of being a felon in possession of a firearm and two counts related to immigration violations.
He faces a potential life sentence on several of the counts if convicted, including the allegation that he killed Fox. Several of the firearm charges also carry potential penalties of life in prison.
A one-week trial is scheduled to begin in November.