(CNN) -- Prosecutors will seek the death penalty against a former California Sunday school teacher accused of killing an 8-year-old girl earlier this year.

Sandra Cantu's body was found in a suitcase in an irrigation pond near where she lived.

Melissa Huckaby, 28, was indicted last month in the death of Sandra Cantu, a playmate of Huckaby's daughter. Huckaby lived in the same mobile home park as Cantu and her family in Tracy, California.

Sandra's body was found April 6, stuffed into a suitcase and submerged in a pond at a dairy farm. She was last seen alive March 27 in the mobile home park.

Huckaby is charged with kidnapping and murdering Sandra, according to the indictment, along with lewd and lascivious acts on a child under 14 and rape by instrument. She pleaded not guilty in June, but entered another not guilty plea on Thursday at a hearing, minutes of which were provided to CNN by a court spokeswoman.

Prosecutors said at the hearing Thursday they plan to seek the death penalty.

Huckaby is the granddaughter of Clifford Lane Lawless, pastor of Clover Road Baptist Church near the mobile home park, and she taught Sunday school at the church, police said.

The church was searched as part of the investigation into Sandra's disappearance and death.

Before her arrest, Huckaby acknowledged to a newspaper reporter that she owned the suitcase that contained Sandra's body, but said it had been stolen.

In addition to the charges in Sandra's death, Huckaby is charged with attempting to poison two people, including a 7-year-old girl. A complaint alleges she "did willfully and unlawfully mingle a harmful substance with food or drink" with the intent to harm the child.

The complaint identifies the child only as "Jane M. Doe." Huckaby is also charged with one count of child abuse endangerment regarding the girl, who the complaint says was in her "care and custody." The other alleged poisoning victim was identified as Daniel Plowman, but no other information was provided.

A gag order has been imposed on parties in the case. Superior Court Judge Linda L. Lofthus has also sealed documents in the case, including the autopsy and toxicology reports and documents relating to a defense motion to exhume Sandra's body.

Huckaby remains jailed without bail. A hearing was set for September 25.

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