Two other men were sentenced to death for the murder of the Naperville girl. But their convictions were overturned.
A court order forbids attorneys from speaking openly about the case.
"I'm not going to talk again until this case is over," said Joe Birkett, DuPage Co. state's attorney.
"We have no comment at this time. Everything we have to say, we'll say in court," said Steve Greenburg, defense attorney.
In court, the judge heard gruesome details of the murder of Jeanine Nicarico. And in open court Brian Dugan pleaded guilty to the crime.
It is a blind plea agreement where the state had not agreed to the punishment. In fact, the DuPage County state's attorney will pursue the death penalty.
Judge George Bakalis asked Dugan if he understood that the death penalty was an option. Dugan replied, "I understand it's a possibility."
In 1983, 10-year-old Jeanine Nicarico was in her Naperville home sick from school. It's alleged Dugan broke into the home, beat and assaulted the girl. Her body was found two days later 7 miles from her home.
The Nicaracos have since moved out of state.
Jeanine's father spoke with ABC7 by phone on Tuesday night.
"It just seems to me that what this is really about is Dugan is looking for mercy in order to avoid the death penalty," said Tom Nicarico.
Dugan is already serving two life sentences for two other murders.
Tom Nicarico says Dugan should get the ultimate punishment for Jeanine's murder.
"In my mind, another life sentence for him is no punishment at all. He's already serving two of them so the only thing that is punishment is the death penalty. He's earned it," said Nicarico.
Criminal attorney and law professor Daniel Coyne says, despite the plea and the desire of the victim's family, 12 jurors would have to unanimously have to agree that death is an appropriate sentence in order for him to receive the death penalty.
"All 12 people would have to agree on a death verdict. If 11 people agree and one does not, it becomes a default life verdict. So a life imprisonment sentence is a very real possibility," said Coyne.
Brian Dugan asked to make a statement in court on Tuesday, but the judge said it was not the appropriate time for his statement.
His statement, obtained by our news partner the Daily Herald, reads in part: "I never imagined it would take a quarter century to stand where I am today to take responsibility for the horrible crimes I committed so long ago. I deeply regret all the pain and suffering I caused. I sincerely hope this brings the Nicaricos and the community a small measure of resolution in their search for the truth."
A jury will be selected in September to determine sentencing.