Photo Of Antinette Keller (Facebook Photo)

Photo Of Antinette Keller (Facebook Photo)

Updated 04/03/13 – 5:19 p.m.

DEKALB, Ill. (CBS) — The man accused of killing a Northern Illinois University freshman and burning her body 2 ½ years ago has been sentenced to 37 years in prison, after agreeing to plead guilty on Wednesday.

William “Billy” Curl had been scheduled to stand trial next week for the murder of Antinette “Toni” Keller, an art student at NIU, in October 2010. He had been charged with first-degree murder, criminal sexual assault and arson in connection with Keller’s death.

When Curl walked into the courtroom, his sister started crying, then shouted “Billy, don’t take it! They’re railroading you!” She continued yelling as she was escorted out of the courtroom.

William "Billy" Curl has pleaded guilty to killing NIU student Toni Keller in October 2010. (Booking Photo)

William “Billy” Curl has pleaded guilty to killing NIU student Toni Keller in October 2010. (Booking Photo)

Under the plea agreement, Curl must serve the entire 37-year term in prison, but will receive credit for 889 days he has spent in jail so far.

Keller’s family was not happy with the plea deal either, but were not in court.

Mary Tarling, a spokeswoman for Keller’s family, said they’re in shock over the plea deal.

Tarling said the family only learned of the plea deal on Monday, and after months of delays, they had been preparing themselves for the trial next week.

She said skipping the trial spares the family of the ordeal, but also the opportunity to honor Keller with her day in court.

DeKalb County State’s Attorney Richard Schmack defended the plea agreement, and said he doesn’t feel he let Keller’s family down.

“No, I don’t. Our job is to get a conviction for first-degree murder, and we did that,” he said. “I could never say that we’ve let the family or community down by getting a conviction for first-degree murder for a murderer.”

He also said, while he had a solid case against Curl, an acquittal is always possible in a jury trial, and even a guilty verdict wouldn’t have guaranteed a longer sentence for Curl, who faced 20 to 60 years in prison if he had been convicted at trial.

Former DeKalb County State’s Attorney Clay Campbell, who built the case against Curl, said he’s deeply saddened by the plea deal.

“It’s outrageous to know that at some point in time in the future, Mr. Curl has the opportunity to be a free man again,” he said. “It diminishes human life, and it dishonors the memory of the victim to know at some time in his 70s, Mr. Curl will actually be released from the Illinois Department of Corrections. I’m not sure any parent that had this happen to their daughter would accept that. I certainly couldn’t accept it if it happened to my kids.”

Curl’s public defender, Tom McCullough, negotiated what’s known as an Alford plea, which allows Curl to maintain his innocence, while agreeing that the evidence prosecutors had against him would have resulted in a conviction at trial.

“He still maintains his innocence,” McCulough said. “People make their own decision when it comes time to fish or cut bait.”

He allegedly attacked Keller, 18, as she walked in Prairie Park, near the NIU campus, on Oct. 14, 2010. He then allegedly burned her remains, which were found two days later, and identified through a DNA match.

CBS 2’s Derrick Blakley reports Curl has admitted to burning Keller’s body, but claimed she died from a seizure following consensual sex in the park.

Curl will be 71 years old when his sentence is complete.