COEUR d'ALENE - The Idaho Supreme Court vacated Joseph Herrera's murder conviction for the shooting death of his 18-year-old girlfriend Stefanie Comack in St. Maries.

A 1st District Court jury in Coeur d'Alene convicted him two years ago of the Christmas day 2011 killing. The trial was moved to Coeur d'Alene from St. Maries to find jurors who were not connected to the two families.

In August 2013, 1st District Court Judge Fred Gibler sentenced Herrera to 22 years to life in prison for second-degree murder.

Herrera appealed, saying testimony at trial by prosecution witnesses was unfair to his side.

"It's a matter of doing the trial over again," Benewah County Prosecutor Doug Payne said Wednesday afternoon.

Payne anticipates Herrera will be transported back to Benewah County from prison.

He said he spoke with members of Comack's family after the Supreme Court's decision was published Wednesday.

"They are prepared to do what's necessary to see this through," Payne said.

Herrera argued in his appeal that four witnesses at trial gave inappropriate testimony concerning alleged prior acts by him and hearsay statements allegedly made by Comack in the weeks leading up to her death.

Prior to trial, the District Court conducted hearings to address the admissibility of certain evidence, including testimony by Comack's family and friends that she had bruising caused by Herrera prior to the shooting.

The court ruled that no testimony would be allowed regarding the bruising because it would have an unfair prejudicial effect.

Comack's sister, Kaytlin Comack, however went on to testify that Stefanie Comack had handprint-shaped bruises when she showed up to a dinner around Thanksgiving day 2011.

"We agree that testimony suggesting Herrera was abusive is highly prejudicial," Chief Justice Jim Jones wrote in the court's opinion.

Jones also said the District Court shouldn't have allowed testimony by Eunice McEwen, Stefanie Comack's friend, that one week before Comack was killed Herrera put a gun to Comack's head and threatened to kill her.

Gibler allowed the testimony with a limiting instruction that it was only to be considered as evidence of Comack's state of mind.

"Eunice's testimony didn't contain any statements of Stefanie's state of mind, and it was highly prejudicial to Herrera," Jones wrote. "Allowing testimony about an event so similar to the state's version of the facts makes it especially likely that the jury would not be able to make a decision on Herrera's state of mind at the time of the shooting without considering the testimony about him having intentionally threatened to shoot Stefanie in the past."

"The issue (the Supreme Court was) wrestling with is a very difficult one," Payne said. "It was very, very difficult to separate the facts from the feelings" in some testimony.

Stefanie Comack's father's girlfriend, Bobbie Joe Riddle, testified that Comack told her Herrera had slapped and choked her.

That testimony was also prohibited, and the two sides were told that in a previous hearing.

The prosecution's questions to Riddle "were specifically designed to elicit testimony regarding those matters the trial court had previously ruled inadmissible," the court said.

Stefanie Comack's mother, Susie Comack, testified that her daughter had told her Herrera is "'psycho.'"

"It appears from the record that the majority of the state's asserted state-of-mind evidence was simply an attempt to present to the jury Herrera's alleged past conduct," Jones wrote. "Despite the court's order, the state asked questions that appeared to be deliberately designed to elicit the exact testimony that the District Court had specifically prohibited."

"I'm not surprised about the ruling," said James Siebe, Herrera's trial attorney.

Jurors were heavily influenced by the prohibited testimony, he said.

"It was killer - it hurt us," Siebe said. "It made the jury think more about that than the facts of the case."

The Supreme Court found Herrera was denied a fair trial, and sent the case back to District Court for further proceedings.

The other four justices concurred with Jones' opinion.

Herrera was accused of killing Comack in an upstairs bedroom he was staying in at his parents' home in St. Maries. The two had been arguing that morning.

Herrera testified at trial that Comack was shot through the forehead by accident.