NEW YORK (CBSNewYork/AP) — The 6-year-old brother of a New York City girl found drugged, beaten and starved testified Thursday in the murder case against their mother, saying that his little sister was rarely fed and was tied to the bed before her death.

Tymel Pierce spoke from a closed-circuit TV in another part of the Brooklyn court as his mother and jurors watched. He could not see them. Wearing a crisp white shirt with a vest and tie, Tymel sat with wide eyes, often sucking his fingers while answering prosecutors with short, soft-spoken sentences.

Court Photo: Ties On Marchella Pierce's Bed (credit: Juliet Papa/1010 WINS)

Asked by Assistant District Attorney Perry Cerrato what happened to his 4-year-old sister Marchella, the boy said: “I asked my mom what happened and she said my sister fell down the stairs.”

His mother, Carlotta Brett-Pierce, cried during most of his testimony. At times, she silently talked back to the screen, once mouthing, “I love you,” CBS 2’s Pablo Guzman reported.

She is charged with murder in the death of her daughter. The girl’s grandmother, Loretta Brett, is also on trial. Both women have pleaded not guilty.

The grandmother’s attorney told CBS 2’s Guzman she cross-examined the little boy so she could establish that the father, who might also testify against the women, should not be let off the hook.

“The government has been trying to portray that the father did not live in the house,” attorney Julie Clark said. “And he clearly — from the words of his own son — was living in that house, taking care of the children. And they are now trying to shift the legal duty on my client. That is the legal duty of the parent.”

Marchella was found dead in September 2010. She was tied to her bed, beaten, drugged and starved, prosecutors said. At the time of her death, prosecutors said her stomach contained one kernel of corn.

With his testimony, prosecutors were trying to show that the girl was singled out for abuse while her siblings were cared for. Tymel also testified that he saw his mother give adult sleeping pills to Marchella.

One of the toughest moments in the courtroom was when the prosecutor asked the boy about life now, with his “new mommy,” as he called her, referring to the boy’s foster mother, versus life before with the woman he called his “old mommy,” Guzman reported.

The boy often responded to prosecutors’ questions by saying he didn’t know the answers. When pressed on whether he didn’t remember or didn’t want to talk about it, he would often reply that he didn’t want to talk about it.

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