The disappearance of Rosella Atkinson remained a mystery for nearly 18 years - until a tormented Brian Hall walked into a police station in 2005 and confessed to her killing.

"My conscience is eating at me, and I know that it's time to get right," Hall told Homicide Detective Aaron Booker later that day.

Yesterday, Hall, 55, of Germantown, pleaded guilty in Philadelphia Common Pleas Court to strangling the 18-year-old Nicetown girl - and now a jury of nine men and three women is poised to decide the degree of his guilt.

He could be convicted of first-, second- or third-degree murder, or maybe voluntary or involuntary manslaughter. Common Pleas Court Judge Shelley Robins New is expected to instruct jurors today on the specific charges they may consider.

Atkinson disappeared from the front steps of her parents' home in October 1987, but her body wasn't discovered until 1988, when a teenager came across her skeletal remains in a field near Central High School.

The remains went unidentified until 1990, when her family went to an exhibit of forensic sculptor Frank Bender - and saw Atkinson's face on one of his pieces.

"It hit us all at the same time - we could see her. It looked like her," Atkinson's mother, Freedeina Carney, told the jury yesterday.

Even after the girl was finally identified, though, the case remained unsolved, until the early-morning hours of Sept. 29, 2005.

That's when Hall walked into the 14th Police District and told Officer Nicholas Cessna that he wasn't crazy - and that he wanted to confess to a murder.

Booker told the jury that later, down at Homicide, Hall explained that he kept seeing the dead girl's face flash in his mind.

"It was an accident - I didn't mean to do it. I'm sorry. I had to have some closure," Booker said Hall told him that day.

Booker said Hall told him he had been drinking at the bar two doors down from Atkinson's home and had gone with her to the field near Central High.

Booker said Hall couldn't remember whether they had sex and said he had blacked out. When he woke up, Booker said Hall told him, he noticed money missing from his sock and got into a scuffle with the girl.

"That's when I put my hand around her neck. I guess I was a little too rough on her," Booker quoted Hall as having told him.

And then, Hall told Booker, he realized that she was dead.

Hall's defense lawyers contend that the crime doesn't amount to first-degree murder, which requires premeditation and a specific intent to kill.

"It's not clear that he was even thinking at the time he committed this killing," Assistant Public Defender Helen Levin told the jury.

But Assistant District Attorney MK Feeney told the jury that it takes several minutes to choke someone to death - and that means he had a specific intent to kill.

"He choked the life out of her," said Feeney, who contends that the crime amounted to first-degree murder.

Defendants in murder cases not involving the death penalty have the right to enter an open plea and to have the degree of guilt decided in court.

While Hall had wanted the judge to make that decision, the prosecution chose to have a jury decide - a new option for prosecutors under recently established case law.

Contact staff writer Emilie Lounsberry at 215-854-4828

or elounsberry@phillynews.com.