Prosecutors may include shocking rape and molestation charges, in addition to murder, in the case against the female Sunday school teacher accused of killing an 8-year-old Northern California girl and putting her body in a suitcase.

Melissa Huckaby, 28, will be in court Tuesday afternoon for her arraignment in the kidnapping and murder of Sandra Cantu, a friend of her 5-year-old daughter's.

Formal charges have not been filed, but San Joaquin County Deputy District Attorney Robert Himmelblau said Monday a murder charge against Huckaby could include the special circumstances of rape with a foreign object.

Lewd and lascivious conduct with a child and murder in the course of a kidnapping might also be a part of the case against Huckaby. Such conditions will mean Huckaby could be sentenced to life in prison or death if she's convicted.

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Huckaby was arrested Friday; police said they don't know her motive and believe she acted alone. Her arraignment is set for 4 p.m. EDT (1 p.m. PDT), and is expected to be attended by an onslaught of journalists.

Only 20 seats have been allotted for reporters — some of them chosen by lottery and some assigned by officials — in addition to space for two television cameras and a few others using other media equipment.

A decision on which, if any, special circumstances to include in the charges hasn't been made, but a conviction on any of them would make Huckaby eligible for the death penalty or life in prison without parole, Himmelblau said.

The district attorney's office hasn't determined whether to seek the death penalty, he said.

Huckaby's family was shocked by the latest disturbing allegations against her.

"That is not my daughter. My daughter is a loving mother," her father, Brian Lawless, told KTVU. "I cannot comprehend that she would do anything like that. That is not my daughter."

Huckaby's family visited her late Monday at the San Joaquin County Jail, where she is being held without bail.

"We're in shock," her distraught father said.

Lawless said during the visit, the family cried and prayed together.

Sandra disappeared on March 27. A massive search ensued and pictures of her were posted all over Tracy, a city of 78,000 people about 60 miles east of San Francisco.

On April 6, Sandra's body was found in a suitcase by farmworkers draining an irrigation pond located only a few miles from Sandra's home in the Orchard Estates Mobile Home Park.

Huckaby lived with her grandparents five doors down from Sandra in Tracy. The little girl was a playmate of Huckaby's 5-year-old daughter, Madison.

Police have not said how, where or why Sandra was killed, but Sgt. Tony Sheneman said investigators believe she acted alone.

"We have not been provided with one (a motive)," Sheneman said Monday. "We don't know why a mother would kill another mother's child."

Neither Himmelblau nor Sheneman would provide details on any evidence leading prosecutors to consider the sexual assault allegations.

"I was hoping that wasn't the case," Sandra's aunt, Angie Chavez, said through tears. "I'm in shock. The whole thing is unimaginable."

In the days after Sandra's body was found, investigators searched Clover Road Baptist Church, where Huckaby volunteered as a Sunday school teacher and her grandfather, Clifford Lawless, is the pastor.

Investigators also interviewed the pastor and seized items from his home. Her family has said they do not know what police were looking for.

On Sunday, outside the church after Easter services, Huckaby's relatives described her as a loving mother with a strong religious upbringing.

"The allegations are so far outside what I know about my niece," Huckaby's uncle, Brett Lawless, 48, of Lakewood, said. "Of course there are doubts in my mind. But we understand the police doing their jobs might have some probable cause."

In 2006, Huckaby was convicted of petty theft in Los Angeles County.

Separately, in January, she pleaded no contest to a petty theft charge in San Joaquin County Superior Court. She was sentenced to 3 years probation on the condition that she participate in a county mental health program.

Himmelblau was not aware if Huckaby had an attorney.

Click here for more on this story from KTVU.com.

The Associated Press contributed to this report.