The mother of a 7-year-old girl beaten to death by her stepfather provoked her husband to abuse the child and did nothing to help as her daughter — cold, naked and battered — lay dying on their apartment floor, prosecutors charged Thursday.

In an abuse case that cast a spotlight on New York's troubled child welfare agency, Nixzaliz Santiago went on trial in Brooklyn state court on charges of second-degree murder, manslaughter and reckless endangerment in the death of her daughter, Nixzmary Brown. She has pleaded not guilty.

The incident two years ago shocked the city, hastened child welfare reforms and made Nixzmary's name synonymous with child abuse. The girl was so malnourished when she died that she weighed only 36 pounds — about half the weight of an average girl that age.

In opening statements, the prosecution sought to portray Santiago as a heartless mother who allowed her husband to abuse the girl as she cared for her five other children.

But defense lawyer Sammy Sanchez portrayed Santiago herself as a victim — a loving but "unsophisticated" mother with a "fifth-grade education" who relied on men for support.

He also hinted she had emotional problems, telling the jury of 10 women and two men how she took a fetus home from the hospital after a miscarriage and put it in a jar in her bedroom.

Sanchez blamed Nixzmary's death on the girl's stepfather, Cesar Rodriguez, who is serving up to 29 years in prison after being convicted of manslaughter in March for delivering the fatal blow that killed the girl. He dodged a murder charge that could have sent him away for life.

Sanchez said Rodriguez became increasingly violent after losing his job in 2005, and Santiago had no choice to but to stay. "She didn't want to go back to a shelter. She had a dilemma," he said.

Prosecutor Ama Dwimoh, who also tried the case against Rodriguez, contrasted the two cases, saying Rodriguez's centered on what he did while Santiago's was about what she didn't do.

"The last words of 7-year-old Nixzmary Brown, moaning in pain and gasping for air, were, 'Mommy, mommy, mommy,"' Dwimoh said. "She didn't love or comfort, and she didn't stop the beatings and she didn't get any help."

Nixzmary died Jan. 11, 2006 of a vicious blow to the head while being punished for stealing yogurt. Santiago reported finding the child unconscious in the family's three-bedroom apartment.

Investigators discovered she had been a virtual prisoner, confined to a room with dirty mattresses, a broken radiator, an old wooden school chair she was bound to with a rope, and a litter box she was forced to use instead of a toilet.

There had been warning signs for years before Nixzmary's death. School employees had reported that she had been absent for weeks the previous year. Neighbors noticed unexplained injuries and noted the child appeared underfed and small for her age. Child welfare workers had been alerted twice but said they found no conclusive evidence of abuse.

The trial was to continue Friday.