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WEST CHESTER, Pa. (CBS/AP) – A man who pleaded guilty to fatally shooting a recent high school graduate during a road rage incident in Chester County learned his fate on Thursday. David Desper will be spending the next 20 to 40 years behind bars in the death of 18-year-old Bianca Roberson.

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Desper, of Trainer, Delaware County, shot Roberson in the head in West Goshen Township last year after they jockeyed for space on a highway merger.

The emotional sentencing lasted several hours as Roberson’s family, prosecutors, and the judge were in tears. Even Desper’s defense attorney could not hold back tears.

During sentencing, prosecutors talked about the day Roberson was killed in June 2017. They say it started as one of the happiest days of her life, as the recent Bayard Rustin High School graduate went shopping with her mother and grandmother at a West Chester Walmart for college supplies.

Roberson’s mother told her daughter to drive straight home because she had a surprise for her, but she never made it because she was gunned down by Desper in a road rage shooting, prosecutors said.

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Roberson’s father, Rodney Roberson, told the judge his daughter had a promising life ahead of her. She was weeks away from heading to college on a full scholarship as she was hoping to be in the FBI one day.

He asked Desper, “Why did you pull that trigger and kill my daughter? Was it because she was young? Because she was black? Because she was a woman? Because you wanted to go first in a lane?”

Desper later told the court he “was just afraid. Her car swerved at me a few times, I squeezed the gun, couldn’t believe what happened. Though, ‘Why is this happening to me?'”

Desper fled the scene and turned himself in four days later. His attorney asked the judge to see leniency in that, but the Roberson family pleaded for the maximum sentence.

At the end of the hearing, the judge said in a tearful statement, “I listened to everything that was presented here. Mr. Desper, I believe you are sorry. I believe you would take it all back if you could. I don’t believe you were afraid. If you are afraid when driving, you hit the break.”

The Desper and Roberson families left the court agreeing with the judge’s sentencing.

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(© Copyright 2018 CBS Broadcasting Inc. All Rights Reserved. The Associated Press contributed to this report.)