"I'm very happy," Weber County Attorney Dee Smith said outside of court after the verdict was read. "I'm just very happy for the family. They have some closure now."
Millerberg faces up to life in prison when he is sentenced on March 18.
"He's disappointed," Millerberg's attorney, Randall Marshall, told the news media after the verdict. "I expected some of it [guilty verdicts on some charges], but I was a little disappointed in some of it."
Millerberg, 38, was accused of injecting Rasmussen with methamphetamine and heroin in his North Ogden home on Sept. 10, 2011. After the girl died of an apparent overdose, Millerberg and his wife, Dea Millerberg, decided to get rid of the body, prosecutors said.
In his closing argument Friday afternoon, Smith urged the jury to finda Millerberg guilty of all charges.
"We're not here because of the choices Alexis made," he told the jury. "We're here because of the choices the defendant made."
Smith argued that the Millerbergs should have been a good example to Alexis, instead of giving the teen drugs and having sexual contact with her.
"We understand that children are vulnerable," Smith said. "That's why we have laws to protect children. We have laws that say, basically, keep your hands off our children."
On Wednesday, Dea Millerberg took the stand and testified against her husband of nearly 10 years.
She recounted that on Sept. 10, 2011, she picked up Alexis to baby sit their kids, but instead she got high with the teen and her husband.
Through the night, Eric Millerberg injected Alexis three times, Dea Millerberg testified once in the teen's neck. The three also attempted to have sex together, the woman testified, but they were too high.
Shortly after her husband injected Alexis for the third time, Dea Millerberg testified that the teen began to complain of being cold and shaky. The teen took a bath, and afterward, the Millerbergs helped her into the couple's bed, then went outside to smoke.
When they returned, they found that Alexis was not breathing. Dea Millerberg said she attempted CPR, but the girl never responded.
In a panic, the Millerbergs weighed their options. Ultimately, they decided to dump the teen in a remote part of Morgan County near the Taggart exit of Interstate 84.
While Smith pinned the girl's death on Eric Millerberg during his closing argument, defense attorney Marshall attacked Dea Millerberg's testimony, saying it was inconsistent.
He argued that it may have been Dea Millerberg who injected the drugs into Alexis, and her husband got involved only after the girl died and Dea Millerberg asked for help.
"Because a little girl got in trouble, a big girl got in trouble," Marshall told the jury.
But Smith rebutted, saying that while Dea Millerberg had a hand in the crime, the jury should stay focused on her husband's alleged crimes.
"There's only one person on trial today," he told the jury. "You are only here to decide the guilt of one person and that's the defendant. Somebody else on another day will decide Dea's guilt. That's not your job."
The defense did not put any witnesses on the stand during the trial, and Eric Millerberg did not testify in his own defense.
Alexis was missing for 38 days before Eric Millerberg's friend, Eric "Peanut" Smith, broke the case for police. He testified that he helped Eric Millerberg move the body on Sept. 12, 2011 a day after the Millerbergs dumped Alexis' body in a heavily wooded area near Taggart.
Eric Smith, handcuffed and in a jail jumpsuit, led police back to the girl's badly decomposed body in October 2011.
The girl was found with her legs folded against her in a fetal position, her lower half stuffed into a garbage bag.
Utah assistant medical examiner Joseph White testified on Friday that the girl's body was so badly decomposed, it was difficult to identify her. Dental records and a fingerprint analysis finally led to a positive identification.
Because Alexis' body was exposed to the elements and animals, White said it was also difficult to examine whether the girl's body had any evidence of trauma.
While toxicology tests determined the teen's body tissue contained lethal amounts of methamphetamine, White said he was unable to determine a cause and manner of death.
Toxicologist Douglas Rollins testified that after looking at the girl's toxicology report, he believed Alexis consumed meth less than 24 hours before she died.
"I am of the opinion that it was probably ingested within hours of her death," he said.
Dea Millerberg, 40, is charged with desecration of a human body related to the girl's death. Her trial is scheduled for April. She was granted "use immunity" in her husband's trial, meaning her testimony can't be used against her in her case.
Charges were never filed against Smith, as he had made a deal with police that if he led them to the girl's body, he would not be charged.