FAYETTEVILLE, Ga. -

Two teenage girls accused of stabbing one of the girls' grandparents to death pleaded guilty Thursday to murder during a court hearing, ending a case that garnered national headlines.

Holly Harvey, 15, was sentenced to two life sentences in prison after pleading guilty to two counts of malice murder. Because of her age, she was not eligible for the death penalty.

She will not be eligible for parole until after she serves 20 years in prison.

Sandy Ketchum, 16, who has been described as Holly's lover, was sentenced to serve three life sentences to be served consecutively.

At the end of her hearing, which lasted less than 10 minutes, Fayette County Superior Court Judge Johnnie Caldwell sentenced her to three life sentences for murder and armed robbery, to be served concurrently -- meaning she could be eligible for parole in 10 years.

During the court proceeding, the girls spoke about the stabbings, and the blood, which Harvey said felt like a bucket of hot water.

Carl Collier, 74, and his wife, Sarah, 73, were each stabbed multiple times Aug. 2 inside the couple's house in north Fayette County. The girls then allegedly fled in the Colliers' truck and were arrested the next day in Tybee Island.

As part of her plea, Harvey detailed how she killed the couple. For half an hour, she choked back sobs and spoke softly as she recounted the killings to Fayette County Superior Court Judge Pascal English.

Harvey and her friend had stayed out all night and spent the morning of the killings listening to music in the basement bedroom of her grandparents' north Fayette home.

That was when Ketchum suggested stealing the grandparent's truck "to get something to calm us down," Harvey said.

"'We'll have to kill them to do that,"' Harvey said she responded.

"But I didn't mean nothing by that," she told Judge Pascal English.

Ketchum suggested hitting them in the head with a lamp, and then suggested getting a knife, Harvey said.

"I got the biggest knife I could find out of the kitchen," she said, adding that they practiced stabbing a mattress to see if the knife was sharp enough.

When the grandparents came downstairs to get a suitcase, Harvey said she stabbed her grandmother.

"My eyes were closed the whole time," she said.

Her grandfather then pinned her down and Harvey said she stabbed him in the chest. She pursued him as he ran upstairs and tried to call for help, pulling the phone out of the wall, Harvey said.

"He grabbed the knife and I thought he was going to stab me," Harvey said, adding she took the knife from him and started attacking him.

When the judge asked Harvey why she did it, the teen said, "For Sandy," and added, "So that we could be together."

Judge English asked Harvey after sentencing her if 20 years in prison "was a good deal" for killing her grandparents. She answered no.