Kathy Patton explained Wednesday in court that she was tired and on illegal drugs when she arrived at her stepsister's house the morning of Feb. 6, 2006, to baby-sit.

Five-month-old Christian Dircio started crying and wouldn't stop, and there was nothing she could do to comfort him, Patton told District Judge Elizabeth Halverson.

"I just got so frustrated, I just threw him on the floor. I didn't mean to kill him. I didn't mean to," Patton, 29, said through tears.

She did not specify what drugs she was on when she killed the infant.

She pleaded guilty Wednesday to second-degree murder and one count of child abuse resulting in substantial bodily harm.

She is expected to be sentenced April 11, but Marc DiGiacomo, deputy district attorney, and Patton's defense attorney, Andrea Luem, have agreed upon a prison stay of 15 years to life for the two counts.

According to grand jury transcripts, the boy's skull was fractured, and his death was caused by blunt force trauma to his head.

Patton called Dircio's mother, Tia Green, about 8:30 a.m. that day and said Christian was not breathing.

Paramedics arrived at Green's home on the 3300 block of Warnock Road, near Decatur Boulevard and Desert Inn Road, and took him to University Medical Center, where doctors removed him from life support two days later.

Patricia Johnson testified to the grand jury that she could hear the infant crying outside Green's home the morning of Feb. 6 as she took her own children to school. The bus stop to school was in front of Green's home.

"He was screaming bloody murder," she said.

Johnson said she saw Patton holding Dircio in her arms in the garage area as he was crying.

"She had him by the tummy, and she was rocking him roughly," Johnson told the grand jury.

Patton appeared nervous, she said.

"She was pacing," Johnson said. Then Patton went back inside, slamming the door behind her.

Dircio's mother, Green, who is Patton's stepsister, was present in court Wednesday, with Patton's father and stepmother. They hugged after Patton's court appearance and left the courthouse, declining to speak to news media.

Patton's father was there to support her, Luem said in the hallway outside the courtroom.

"The family has been real divided over the whole thing," she said.