Three children testified against Estell, 40, at his preliminary hearing, but detectives believe there may be more than a dozen child victims they have yet to identify.
The testimony of the three boys and law enforcement officers was enough to persuade a judge to order Estell to stand trial.
"He made friends with these children in order to commit a sexual offense," Deputy Salt Lake County District Attorney Coral Sanchez said. "And he got away with it for many years until recently."
But Estell's defense attorney Nick Falcone said authorities investigated these allegations years ago but did not file charges then. The lawyer said there is not enough to convict Estell of the charges against him: four counts of aggravated sexual abuse and one count of sodomy on a child, all first-degree felonies.
Defense attorneys argued the boys' stories didn't add up then and now and police believed the children were lying.
"I'm taken aback that there are so many allegations against Mr. Estell with no evidence to back it up," Falcone said, adding the prosecution's case is "circumstantial" and the witness testimony "inconsistent and unreliable."
Detective Scott Moutgos testified that he didn't know why the 2008 cases were not prosecuted after they were reported. He said he began looking into the cases after he spoke with Estell in 2012 in connection with a suspected probation violation.
During that interview, Estell admitted to molesting the three boys in 2008, Moutgos said. Estell also told detectives there had been other boys as many as 18 over the course of 20 years, Moutgos said. The tape of that 2012 interview was not played during Thursday's preliminary hearing.
The boy Estell is accused of molesting at the 2008 sleepover in a neighbor's apartment testified that Estell was known as a child molester at the apartment complex where he and Estell lived, at 176 N. Redwood Road.
"I heard rumors from every single one of my friends ... he's a pedophile, a person who touches little kids," the now-15-year-old said. "I didn't believe my friends, you know? You don't believe it until it actually happens to you."
Another neighborhood boy Estell is accused of molesting in 2008 testified that Estell would frequently "wrestle" with children in the apartment complex. He said Estell touched his genitals while they were wrestling in the neighborhood.
"It happened a couple of times," said the alleged victim, now 15. "I told him I didn't want to play no more."
But defense attorneys said these two boys assaulted Estell and made up the alleged abuse.
One of the boys was charged in 2008 for allegedly beating and urinating on Estell. Prosecutors said this violence was in response to the alleged sexual assault.
The third boy Estell is accused of molesting did not live in the same neighborhood. They met at an American Idol concert at EnergySolutions Arena in 2008, prosecutors said.
The boy said Estell approached him with concert signs, sat down next to him and began talking about sex. Estell then placed his hands on the boy's thigh and began to rub his leg, over his jeans, he testified.
"It made me extremely uncomfortable, and violated," said the boy, now 17.
The charges in these three incidents were filed shortly after Estell was interviewed at the Salt Lake City Police Department in November 2012.
He was brought in for questioning after he allegedly told his probation officer and therapist about a sexual encounter he had with a young man he believed to be 18, officials testified.
Upon further questioning, Estell said the boy was in high school, witnesses said. At the time, Estell was on probation in connection with a 2010 sexual battery case involving a teen, according to testimony.
"[Estell] said he was tired of living this way," Moutgos testified. "That he was tired of hurting the kids, that he knew it was traumatizing for them, and he wanted to come clean."
Three months before the police interview, Estell allegedly sexually abused a 14-year-old boy at a park near the Jordan River Parkway. Charges in that case were filed last month three first-degree felony counts of forcible sodomy and one count of second-degree forcible sexual abuse.
Estell is scheduled to appear for a preliminary hearing in that case on Tuesday. He will be arraigned on the 2008 charges April 19.
Anyone with allegations against Estell is encouraged to contact the Salt Lake City Police Department's Special Victims Unit at 801-799-3720.