Wesley and Sini Mathews signed relinquishment paperwork for their biological child on Friday during their scheduled final Child Protective Service (CPS) hearing, according to US media reports.
CPS officials had removed her from the Mathews' Richardson home on October 9, two days after her sister Sherin was reported missing.
Sherin's decomposed body was found two weeks later in a culvert close to her home. An autopsy concluded Sherin died of homicidal violence, but how she died could not be determined by the Dallas Medical Examiner's Office due to the decomposition of the body.
The Dallas County capital murder indictment against the father says he killed Sherin "by a manner and means unknown to the grand jury," court records show.
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If convicted, Mathews could face the death penalty, should prosecutors choose to pursue it, or an automatic sentence of life without parole.
Wesley was arrested in October on a felony injury to a child charge after the girl's body was found. He originally told police that he put her outside on October 7 at 3 am because she would not drink her milk. He later changed that story to say that the child choked on her milk.