HOUSTON -- Andrea Yates, the mother accused of drowning her five children, was under suicide watch Thursday night, as Harris County prosecutors began to prepare their case against her.

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Prosecutor Talks About Yates Case

Yates is being held at the Harris County jail and she was charged with capital murder in the deaths of the two oldest children, Noah, 7 and John, 5.

Prosecutors said that charges against Yates in the deaths of the other children are pending, based on what the grand jury says Friday.

Medical Examiner chief investigator Harrell Jordan said that the case has had a widespread effect on the police and prosecutors.

"This has affected everybody," Jordan said. "The police department, the staff, it is just an unbelievable event."

Detectives and spent Thursday investigating Yates' past and gathering information on what led to the drownings.

Prosecutor Kay Lynn Williford said that the Yates case is unique.

"I have had a case where I have had children that have been killed before that I have dealt with," Williford said. "I have never had a situation where I have had five children that were all murdered in a single episode such as this."

The medical examiner's office said that they are waiting on toxicology results before making a definitive ruling on the cause of death.