Autumn Pasquale of Clayton, N.J., was found strangled in a recycling bin near her home after she disappeared last fall.

A teenager admitted Wednesday that he strangled a 12-year-old girl who disappeared last fall while out riding her bike, touching off a massive search that ended when her body was found in a recycling bin just blocks from her home.

Justin Robinson, 16, pleaded guilty to aggravated manslaughter in the death of Autumn Pasquale after agreeing earlier in the day to have his case moved to adult court.

At the hearing, the teen took sole responsibility for killing the girl, even though his older brother is also facing a murder charge, said Camden County Prosecutor Warren Faulk.

Faulk said the boy asked the girl to come to his home to possibly trade bike parts, but he declined to discuss a motive for the killing.

The state was willing to accept a plea deal for charges less than murder because of the complicated circumstances, he said.

Because of the boy’s age at the time of the killing and his “diminished capacity,” it was not a sure thing that a judge would have agreed that the case should be tried in adult court, Faulk said.

While there was forensic evidence that places Autumn’s death in Robinson’s house, there was not clear evidence — other than the boy’s admission — that he was the one who choked the girl to death, the prosecutor said.

Under a plea agreement, Robinson faces a 17-year prison sentence with no chance of parole for more than 14 years when a judge metes out his punishment Sept. 12. Faulk said that if the case had remained in juvenile court, the maximum sentence would have been 20 years, but he would have had a chance of parole in less than seven years.

His brother Dante was 17 at the time and also is charged with murder in the case. His case is pending in juvenile court. Because of a court order, prosecutors and others involved in the case would not discuss those charges.

The public defender representing Justin Robinson did not return a call.

Jaime Kaight, an attorney for Autumn’s mother, Jennifer Cornwell, said prosecutors did “the best they could” in a challenging case.

Doug Long, a lawyer for the slain girl’s father, Anthony Pasquale, said it was hard for him to sit through the sentencing Wednesday.

“Mr. Pasquale knows that no amount of years on a sentence is going to bring his daughter back,” Long said. “The only justice would be to bring Autumn back, but that will never happen.”

Forty-eight hours after the girl went missing Oct. 20, her body was found in a recycling bin near the Robinsons’ home in Clayton, a rural community 25 miles south of Philadelphia.

Authorities had credited a tip from the suspects’ mother with helping them solve the case. They said she saw something in one of their Facebook posts that gave her cause to call police. The call led them to the body and her sons.

Initially, some of the victim’s relatives complained about the search for the girl and the way Gloucester County prosecutors handled the case, which was eventually moved to the Camden County prosecutor’s office.

Autumn’s parents later had a legal squabble over money raised to help their families, but they eventually reached a settlement over that dispute.