Girl, 13, Admits Helping 2 Sisters Kill Woman : Northridge: The neighbor, 62, who befriended the three teen-agers, was stabbed repeatedly. A 17-year-old will be tried in March.

A 13-year-old Northridge girl pleaded guilty Tuesday to helping her two teen-age sisters stab to death a 62-year-old neighbor woman who befriended them.

According to the charges against them, the girl handed a knife to her 16-year-old sister, who used it to stab Meta Francis Murphy repeatedly in November, 1991, while a 17-year-old sister allegedly turned up the volume of a stereo to drown out the victim’s screams.

The youngest girl entered her plea to a charge of second-degree murder just before the start Tuesday of what would have been the second and final day of her trial on first-degree murder charges.

In adult criminal proceedings, pleading guilty to the lesser charge would have lowered the maximum possible sentence to 15 years to life, rather than 25 years to life. But under state law, juveniles can be confined only until their 25th birthday in any case, so the plea to the lesser charge has no effect on the maximum possible sentencing.

The girl’s attorney, Jerome V. Posell, said he recommended she plead guilty to the lesser charge because “it was in her best interest.” He declined to elaborate.

Deputy Dist. Atty. Thomas Rubinson said he agreed to accept the girl’s plea to the lesser charge because it might have been difficult to prove premeditation to get a first-degree murder conviction.

The girl is scheduled to be sentenced March 16 by San Fernando Valley Juvenile Court Commissioner Gary A. Polinsky.

Her 16-year-old sister has already been convicted of first-degree murder and was sentenced Jan. 28 to the California Youth Authority.

The oldest sister is scheduled to go on trial March 10.

Rubinson said he still does not know the motive for the killing.

Murphy, who lived alone next to the sisters on Mayall Street, worked at the Panorama City branch library. She had befriended the girls, often taking them to school or looking after their cats.

According to testimony in the trial of the 16-year-old, Murphy was stabbed 11 times in the back and three times in the chest. Her body was then dumped in a closet and covered with coats.

Her body was discovered by police Nov. 21, 1991, after co-workers at the library reported her missing because she failed to show up for work.

The murder remained a mystery for months until an acquaintance of the sisters told police that she heard the two older girls boasting about the slaying.

Police also tied the sisters to the murder through bloody palm- and fingerprints on the front door of the woman’s townhouse and on a pet gate, prosecutors said.