Mother of 3 boys found abandoned along with remains of their brother says, "I'm sorry. I didn't do it."

Harris County, Texas — The mother of three boys authorities say were found abandoned in their Houston area apartment along with the skeletal remains of their young brother is denying responsibility – and apologizing at the same time.

Gloria Williams, 35, spoke with CBS Houston affiliate KHOU in an exclusive jailhouse interview Thursday.

One of the sons, 15, called the Harris County Sheriff's Department Sunday and said his brother, Kendrick, 8, had been dead for a year and his body was in the apartment, according to the agency.

Deputies found the teen and two brothers, 10 and 7, living alone there, Sheriff Ed Gonzalez said. The 15-year-old told them his parents hadn't lived in the apartment for several months.

Williams is charged with injury to a child by omission and tampering with evidence (human corpse).

Her boyfriend, 32-year-old Brian Coulter, is charged with killing Kendrick.

Investigators say Williams failed to protect them or get them help despite her boyfriend allegedly beating one of them to death and continuing to abuse the others.

Asked what happened, Williams told KHOU reporter Grace White, "I'm sorry. I didn't do it."

When White asked Williams if she knew Kendrick was dead, her response was a simple "No."

But according to court documents, investigators say Williams altered, destroyed and concealed Kendrick's body to get rid of evidence.

When White asked Williams why she left the kids alone, she said, "I checked on them every two weeks."

But when pressed, she didn't want to elaborate.

Melody Robinson, one of the children's paternal grandmothers, said Williams has a total of six kids ranging from 7 to 17. Robinson has custody of one of them, a 13-year-old girl Williams first brought into Robinson's home when she was just 2 weeks old. 

"Her mom was very unstable. She was sleeping on the floor at her grandmother's house with the babies, and so I just asked her to give her to me," Robinson told White.

Robinson said she had no idea Kendrick was dead and the children were abandoned.

She said the last time she saw Williams was last November, when another of Williams' children, a 17-year-old girl, wanted to come live with Robinson because of Williams' boyfriend's behavior.  

"She just got tired seeing him abuse her siblings and when she stepped in to try to protect them, she put her out," said Robinson.

Investigators said Williams and Coulter were arrested outside a public library where they were looking up news articles.

A candlelight vigil for Kendrick is planned for Saturday.