He may testify about what happened in the family's Brooklyn apartment.
Prosecutors accuse mother Carlotta Brett-Pierce of beating and starving Marchella Pierce, and they say the grandmother, Loretta Brett, knew about it.
Earlier this week, jurors were shown grisly images of the emaciated, bruised toddler who was found dead in her Bedford-Stuyvesant home.
Marchella Pierce was found dead in September 2010. Prosecutors say she was tied to her bed, beaten, drugged and starved.
Photos of the dead girl show black-and-blue bruises on her face, arms, and back. Practically every rib was visible through her skin.
At her death, prosecutors say her stomach contained one kernel of corn.
Brett-Pierce and Brett have pleaded not guilty in her death.
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