But mystery and uncertainty still surround the case.
Olsen, who will serve up to 15 years in prison for the crime, claims he saw another man he will not publicly name kill Kiplyn by bashing her twice in the head with a rock.
Prosecutors said Friday they believe the killer is one of the three men who have pleaded guilty to federal perjury charges in connection with the case: Scott Brunson, David Rucker Leifson and Garry Von Blackmore.
Most distressing to the Davises on Friday was the fact that their daughter's remains are still missing. Olsen's cooperation with any search for Kiplyn's remains was not a part of his plea agreement.
"The hardest thing is not knowing where Kiplyn is," her father said during an emotional statement to 3rd District Judge Terry Christiansen.
Richard Davis thanked Olsen for his plea, saying it "brings a little bit of closure to me and my family."
But Davis also begged Olsen to reveal where his daughter is buried.
Davis said he would become the defendant's "biggest advocate" even trying to free him from prison early if he helps bring a final close to "this terrible ordeal."
Kiplyn, a sophomore at Spanish Fork High School, disappeared after her lunch break on May 2, 1995.
Defense attorney Jeremy Delicinosaid Olsen refused to publicly name the actual killer because he is concerned for his safety while serving his remaining prison time.
As a factual basis for Olsen's plea, Delicino told the court that Olsen and the killer drove the girl that day up Spanish Fork Canyon. There, Kiplyn and the killer walked away out of Olsen's sight.
About 35 or 40 minutes later, Olsen claims he heard an argument and went looking for the two.
He then observed the killer strike Kiplyn in the right side of the head with a softball-sized rock. She fell and the killer struck her with the rock again. Olsen said the killer then asked him to move the girl under some trees.
Olsen and the killer drove away, but returned in the early evening to put the girl's body into a vehicle for burial elsewhere.
Friday's plea allowed Olsen, 33, to avoid a possible prison term of up to life in prison. Had Olsen's case gone to trial next month, prosecutors would have relied largely upon seven witnesses who say they heard Olsen claim he killed the girl.
In accordance with the plea agreement negotiated by attorneys, the judge ordered Olsen's state prison time to run concurrently with the 150 months the defendant is already serving in the federal system for lying to investigators about the case. Olsen also was given credit for time he has spent in the Utah County Jail since October 2007, while awaiting resolution of the state case.
Olsen will be free in 2022, even if he serves the maximum amount of time.
Deputy Utah County Mariane O'Bryant said the murder investigation is ongoing, but they are not ready to file additional murder charges.
"We have no body. We have no crime scene," O'Bryant told reporters.
A total of five men have been charged in connection with Kiplyn's disappearance, but only Olsen and Christopher Neal Jeppson faced murder charges.
Jeppson, who was charged in state court with first-degree felony murder, in May 2009 entered a no-contest plea to obstructing justice and was sentenced to prison for up to five years. That sentence runs concurrent with a five-year federal prison term for lying to investigators about Kiplyn's disappearance.
Olsen's trial, originally to be held in Provo's 4th District Court, was moved to Salt Lake County last May. Delicino successfully argued that 15 years of publicity had tainted the Utah County jury pool.
Olsen did not speak in court Friday except to answer questions from the judge regarding the waiver of his trial rights, and to enter his guilty plea.
Delicino said later that Olsen is "deeply remorseful," but had asked him to speak on his behalf in court. Olsen agreed to the plea deal, in part, to bring closure to the Davises and to his own family, Delicino said.
Olsen in the fall of 2006, claimed he could lead investigators to the girl's body, and a federal judge allowed U.S. marshals to take him up Spanish Fork Canyon to search. The body was not found and the judge later called the trip a "charade."
Olsen's attorney at the time, Stephen McCaughey, told news reporters that Olsen did not know where the girl was buried.
"He just wanted a trip and he wanted to see the leaves change," McCaughey said.
Richard Davis said his own efforts to find his daughter's remains have included walking ditches, wading rivers up to his neck and consulting psychics.
"It's been a hard journey," Davis told reporters. "If it sounds like I'm crazy, you're right. I'm crazy to get my daughter back."
Daniel Boothe, of Boothe Brothers Music in Spanish Fork, said Kiplyn's disappearance has occupied the city's collective mind for more than a decade. Many merchants displayed Kiplyn's missing-person poster in their windows for years, replacing them after they weathered too much.
Kara Morris, who moved to Spanish Fork at the same time Kiplyn disappeared and has come to know the Davis family, said the plea provides the community and the family some sense of resolution.
"[Olsen is] finally giving the family some closure," Morris said. "It is good for him to take some accountability."
Now, she said, everyone would like to see Kiplyn's remains recovered and given a proper burial beneath the headstone waiting for her in the Spanish Fork Cemetery.
Federal prosecutors released a statement Friday noting their perjury cases "helped unlock the doors leading to [Friday's] plea."
"Mr. Olsen's stipulation of facts in support of his guilty plea today is the first admission in court of the events that transpired on May 2, 1995," said U.S. Attorney for Utah Carlie Christensen.
Donald W. Meyers contributed to this report.