WOODBURY, N.J. — A New Jersey teenager called his actions "a big mistake" as he was sentenced Thursday to 17 years in state prison for fatally strangling a 12-year-old girl whom he had lured to his home with an offer to trade bicycle parts.

Justin Robinson, now 16, pleaded guilty last month to aggravated manslaughter in a deal with prosecutors who were facing some major challenges in the case, including a lack of physical evidence to determine whether he or his brother Dante Robinson killed Autumn Pasquale in October 2012.

Robinson, who looked mostly straight ahead during the two-hour sentencing hearing, must serve more than 14 years before he is eligible for parole.

"I'm sorry. I never meant for this to happen," he told Judge Walter Marshall. "This was all a big mistake."

Relatives of the girl did not see it that way, and some wanted the judge to issue a tougher sentence than the one agreed to in a plea agreement. If the judge had done so, though, the plea could have been invalidated.

"I believe the defendant deserves more than 17 years," said the girl's father Anthony Pasquale, who as a mail carrier had delivered letters to Robinson's family in Clayton, where the families of the victim and her killer had deep roots. "I believe his fate should be nothing but death."

When he pleaded guilty, Justin Robinson said he acted alone. During a sentencing proceeding, neither he, his lawyers, nor prosecutors shed light on a motive for the killing, or even what happened beyond what was already known: Pasquale went to his house several blocks from hers after receiving a Facebook offer to trade bike parts on Oct. 20. When she didn't return home that night, her family, then the entire community, set off in a frantic search. Two days later, her body was found in a recycling bin behind the home next to Robinson's.

A break in the case for investigators came when the boy's mother, Anita Saunders, called police after seeing something troubling in a Facebook post from one of her sons. Speaking briefly during the sentencing, Saunders told the judge that media accounts of what happened were incorrect. "Nobody knows exactly what happened the day of the accident," she said.

Robinson's lawyer, Jean Faulkner, told the judge that the boy had post-traumatic stress disorder from being physically abused as a young boy and seeing his father strangle his mother more than once. "This is a learned behavior," Faulkner said.

Pasquale's family told the judge about the Autumn, whom they described as a loving tomboy who wore mismatched socks and loved to ride her BMX bike.

They talked about how her disappearance and death touched the town, located 25 miles southeast of Philadelphia. Her old soccer team, once known as the Clayton Comets, is now Autumn's Angels; her jersey number, 14, has been retired from the Clayton Middle School sports teams; a bike path and a park are now named for her.

And they told the judge how members of the family, including her siblings and young cousins, are in therapy and dealing with nightmares about her death.

"When I see the blue recycling bins out, I cry to think Autumn's innocent life was so easily discarded like a piece of trash," said the girl's maternal grandmother, Mary Pasquale, who had taught Justin Robinson in school.

Prosecutors agreed to allow Robinson to plea to aggravated manslaughter rather murder because of challenges with the case. Because of his age and a developmental disability, it was not a sure thing that he would be moved to adult court. If he had been convicted of murder in juvenile court, he could have had a chance of parole in less than seven years.

They also have said that there was no evidence besides his confession that made it clear that it was he and not his brother who killed the girl.

Dante Robinson, who was 17 when he was arrested last October, is still charged with murder in family court. Authorities have not said when they may drop those charges.

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  • Autumn Pasquale

    Photos released by Clayton, N.J. Police Department show Autumn Pasquale, 12, of Clayton, N.J. Police allege that two teenaged brothers murdered Pasquale. (AP Photo/Clayton, N.J. Police Department)

  • Autumn Pasquale

  • People weep at a gathering outside town hall Tuesday, Oct. 23, 2012, in Clayton, N.J., not far from where a body preliminarily identified as a missing 12-year-old girl's was found in a home's recycling bin. The Gloucester County Prosecutor's Office announced early Tuesday that they believed the body of Autumn Pasquale was found around 10 p.m. Monday, in a recycling bin at a home just blocks away from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for the girl's safe return. (AP Photo/Mel Evans)

  • An investigator loads into a police van a BMX bicycle removed Tuesday, Oct. 23, 2012, in Clayton, N.J., from a house where a body identified as missing 12-year-old girl Autumn Pasquale was found. The Gloucester County Prosecutor's Office announced early Tuesday that they believed the body of Autumn Pasquale was found around 10 p.m. Monday, in a recycling bin at a home just blocks away from her house. (AP Photo/Mel Evans)

  • An investigator loads into a police van a BMX bicycle removed Tuesday, Oct. 23, 2012, in Clayton, N.J., from a house where the body of Autumn Pasquale was found in the home's backyard recycling bin. Authorities did not confirm the bike was the one belonging to Pasquale, but it matched the description of the white BMX she was seen riding Saturday afternoon before she disappeared. (AP Photo/Mel Evans)

  • Jody Robinson

    Clayton High school 11th-grader Jody Robinson answers a question Tuesday, Oct. 23, 2012, in Clayton, N.J., about neighbors who live in a home where the body of Autumn Pasquale was found in the home's backyard recycling bin. Police Tuesday removed a bicycle from the home that matched the description of the white BMX Pasquale was seen riding Saturday afternoon before she disappeared. (AP Photo/Mel Evans)

  • Corey Hewes

    Corey Hewes, center, answers a question Tuesday, Oct. 23, 2012, in Clayton, N.J., about neighbors who live in a home where Autumn Pasquale's body was found in the home's backyard recycling bin. The discovery of the body came about 48 hours after her family reported her missing. (AP Photo/Mel Evans)

  • Paul Spadafora, Mary Pasquale

    Paul Spadafora and Mary Pasquale, the uncle and grandmother of Autumn Pasquale sit together at a gathering outside town hall Tuesday, Oct. 23, 2012, in Clayton, N.J., not far from where a body preliminarily identified as the missing 12-year-old girl's was found in a home's recycling bin. The Gloucester County Prosecutor's Office announced early Tuesday that they believed the body of Autumn Pasquale was found around 10 p.m. Monday, in a recycling bin at a home just blocks away from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for the girl's safe return. (AP Photo/Mel Evans)

  • Sean Dalton, Paul Spadafora, Mary Pasquale

    Gloucester County Prosecutor Sean Dalton greets Paul Spadafora and Mary Pasquale, the uncle and grandmother of Autumn Pasquale at a gathering outside town hall Tuesday, Oct. 23, 2012, in Clayton, N.J., not far from where a body that Dalton identified as the missing 12-year-old girl's was found in a home's recycling bin. (AP Photo/Mel Evans)

  • Vicky Armstrong

    Vicky Armstrong cries as she watches police investigate the crime scene on Clayton Avenue in Clayton NJ on Tuesday Oct. 23, 2012, after the discovery of a girl's body in a home's recycling bin. Gloucester County prosecutors say a body believed to be that of Autumn Pasquale was found around 10 p.m. Monday in the bin just blocks from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for her safe return. (AP Photo/ Joseph Kaczmarek)

  • Sean Dalton

    A photograph of Autumn Pasquale is seen as Gloucester County Prosecutor Sean Dalton addresses a gathering outside town hall Tuesday, Oct. 23, 2012, in Clayton, N.J., not far from where a body preliminarily identified as the missing 12-year-old girl's was found in a home's recycling bin. The Gloucester County Prosecutor's Office announced early Tuesday that they believed the body of Autumn Pasquale was found around 10 p.m. Monday, in a recycling bin at a home just blocks away from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for the girl's safe return. (AP Photo/Mel Evans)

  • People weep and listen at a gathering outside town hall Tuesday, Oct. 23, 2012, in Clayton, N.J., not far from where a body preliminarily identified as a missing 12-year-old girl's was found in a home's recycling bin. The Gloucester County Prosecutor's Office announced early Tuesday that they believed the body of Autumn Pasquale was found around 10 p.m. Monday, in a recycling bin at a home just blocks away from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for the girl's safe return. (AP Photo/Mel Evans)

  • A teen who declined to be identified is overcome with grief after visiting the crime scene on Clayton Avenue in Clayton NJ on Tuesday Oct. 23, 2012, after the discovery of a girl's body in a home's recycling bin. Gloucester County prosecutors say a body believed to be that of Autumn Pasquale was found around 10 p.m. Monday in the bin just blocks from her house. (AP Photo/ Joseph Kaczmarek)

  • Tom Bianco

    Clayton Mayor Tom Bianco speaks to members of the news media on Clayton Avenue in Clayton NJ on Tuesday Oct. 23, 2012, after the discovery of a girl's body in a home's recycling bin. Gloucester County prosecutors say a body believed to be that of Autumn Pasquale was found around 10 p.m. Monday in the bin just blocks from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for her safe return. (AP Photo/ Joseph Kaczmarek)

  • An investigators photographs evidence in the back yard of a house on Clayton Avenue in Clayton NJ on Tuesday Oct. 23, 2012, after the discovery of a girl's body in a home's recycling bin. Gloucester County prosecutors say a body believed to be that of Autumn Pasquale was found around 10 p.m. Monday in the bin just blocks from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for her safe return. (AP Photo/ Joseph Kaczmarek)

  • Investigators gather at a house on Clayton Avenue in Clayton NJ on Tuesday Oct. 23, 2012, after the discovery of a girl's body in a home's recycling bin. Gloucester County prosecutors say a body believed to be that of Autumn Pasquale was found around 10 p.m. Monday in the bin just blocks from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for her safe return. (AP Photo/ Joseph Kaczmarek)

  • An investigators walks through the back yard of a house on Clayton Avenue in Clayton NJ on Tuesday Oct. 23, 2012, after the discovery of a girl's body in a home's recycling bin. Gloucester County prosecutors say a body believed to be that of Autumn Pasquale was found around 10 p.m. Monday in the bin just blocks from her house and from Borough Hall, where thousands of people gathered earlier in the evening for a tearful candlelight vigil to pray for her safe return. (AP Photo/ Joseph Kaczmarek)

  • Investigators gather at a house on Clayton Avenue in Clayton NJ on Tuesday Oct. 23, 2012, after the discovery of a girl's body in a home's recycling bin. Gloucester County prosecutors say a body believed to be that of Autumn Pasquale was found around 10 p.m. Monday in the bin just blocks from her house. (AP Photo/ Joseph Kaczmarek)