Half Sister Convicted of Murder She Admitted in Diary : Trial: Schoolmates, relatives and attorney are shocked by the verdict. The conviction means the Bay Area 15-year-old could spend 10 years in custody.

HAYWARD, Calif. —  A Bay Area 15-year-old, who wrote in her diary that she had suffocated her younger half sister, was found guilty of second-degree murder Friday and could spend the next 10 years in custody.

The girl, who disavowed the diary entry during her 2 1/2-week trial, turned stone-faced and stiff in her blue-and-white flowered dress as Superior Court Judge Sandra Margulies announced her decision.

Her schoolmates and relatives erupted in gasps and sobs as the ruling was read in an Alameda County courtroom. The girl’s distraught mother was later rushed to the hospital by ambulance after fainting while fleeing television cameras.

Defense attorney Melvin Belli called the decision one of the “most shocking of my career” and angrily vowed to appeal. “There was no murder here,” said Belli, who characterized the diary entry as the “crazy” concoction of a disturbed adolescent. “This poor girl did nothing wrong. The killer in this case was asthma.”

The prosecutor insisted the gripping account printed on Page 1 of the green journal provided irrefutable evidence the girl had murdered her 4-year-old half sister.

“She gave an accurate, detailed confession of what happened,” said Deputy Dist. Atty. Matthew Golde. Expert testimony that the child had died of an acute asthma attack was “something manufactured by the defense.”

Shortly before his wife collapsed, the defendant’s stepfather read a statement to reporters, berating the district attorney for his courtroom tactics and for subjecting the grieving family to yet another loss.

“We are wounded and disillusioned by a judicial system wherein the truth alone does not seem to be enough to set you free,” he said, flanked by his pastor and relatives. The group then ran from the courthouse, with eight TV news teams in pursuit.

Sentencing was set for July 2. Although the teen-ager could be confined to the California Youth Authority until she turns 25, the judge hinted that she may consider alternatives, such as placement in a group home or psychiatric facility.

Belli said he is likely to push for that sort of sentence, but the prosecutor suggested that he may oppose it.

“She is troubled; she needs help,” Golde said. “But she’s also dangerous. She’s a murderer . . . and should be in a secure setting.”

The case began in the East Bay city of Fremont on Aug. 18, when the girl’s mother and stepfather awoke to find their 4-year-old daughter dead in her bed. An initial coroner’s investigation was inconclusive, finding only that the child had stopped breathing for an unknown reason.

Four months later, the teen-ager ran away from home, prompting the couple to pry open her locked diary in a hunt for clues to her whereabouts. Inside, they found some horrifying words:

“Dear Diary . . . I killed my sister! I went into her room and got her and took her into my room and told her I loved her and covered her mouth and suffocated her! You’re the first person I ever told this to. I feel better.”

The names of the teen-ager and her relatives have been kept confidential because she is a juvenile. She is a freshman at Washington High School in Fremont.

Golde characterized the murder as a sort of mercy killing, arguing that the teen-ager had lived a life of sexual and emotional abuse at the hands of her stepfather and sought to “rescue” her half sister from a similar fate.

A coroner testified that the younger girl had been sodomized at or just prior to her death and bore scars indicating similar abuse during the previous year. Other testimony revealed that the 15-year-old had charged her stepfather with molesting her in 1991. She later recanted, and the stepfather denied on the witness stand that he abused either child.

Asked if he planned to pursue any molestation charges against the stepfather, Golde said: “My door is open” if the convicted girl wishes to initiate a prosecution.

The defense team agreed that their client had lived a tormented life in a “terribly dysfunctional family,” but argued that there was no murder. Instead, Belli presented testimony from a retired UC San Francisco pathologist, who said the child died of a rare, intense attack of asthma she had suffered throughout her life.

The diary entry, according to the defense, was an attempt by the teen-ager to give her anguished mother an explanation for the puzzling death.