The man, who can't be named because of a publication ban, was just 17 when he killed Laura Szendrei.
The now 20-year-old Delta, B.C., resident stood up at the end of his preliminary hearing Thursday and pleaded guilty to second-degree murder in the Grade 10 student's death.
He was originally charged with first-degree murder and the Crown has indicated it wants the man to serve an adult sentence, which could see him spend many more years in prison than if he were sentenced as a youth.
The sun was shining and sporting events were underway on Sept. 25, 2010, when Szendrei's friends heard her screaming from a path way in the park and ran to help her.
She'd had been severely beaten, and died the next morning in hospital.
In the days that followed, Szendrei's parents, Mike and Rachael Szendrei, made a tearful plea for help as residents in the suburb south of Vancouver feared for their safety.
Delta Police received about 500 tips, but the mystery of who killed Szendrei continued for months.
But police had already identified a suspect and went to work on an undercover operation
On Feb. 21, 2011, Delta Police announced the arrest of the 17-year-old in Szendrei's murder.
The police sting that helped get him before a judge was a major factor in that outcome, said Const. Ciaran Feenan, spokesman for the Delta Police Department.
"Needless to say, it was instrumental in the investigation itself and certainly played a factor in what has happened today."
"We put a lot of resources from the onset of the investigation ... to make an arrest and ultimately hold someone accountable for the offence," he said, adding he could not provide any details of the investigation.
Feenan said Szendrei's parents, who endorsed the plea agreement, would not be making a statement Thursday.
"It's been an emotional time for them. It's just ignited the loss of their daughter and reignited the tragedy," said Feenan, who was with the family in court as their daughter's killer pleaded guilty.
"It's going to open up their loss so they're going to take some time as a family to bring some closure to it."
Crown spokeswoman Samantha Hulme said an application has been filed to have the young man sentenced as an adult.
Under the Youth Criminal Justice Act the sentence for such a crime is seven years, with a maximum four years in prison and the remainder of the sentence to be served in the community.
An adult sentence for second-degree murder is automatically life, with a minimum eligibility for parole set at 10 years.
"The next date back in court for sentencing is the 18th of February, for four days," she said.
In the weeks after Szendrei was killed, bushes along the pathway where she was attacked were closely cropped, leaving a clear view between the roadway and the playing fields.
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