A prosecutor in the trial of a mother accused of beating her 2-year-old daughter to death read jurors a note Thursday in which the mother said she couldn't live with herself after her child died.

Galveston County Sheriff's Department Sgt. Elias Cazares testified that investigators searching the suburban Houston home of Riley Ann Sawyers' mother, Kimberly Dawn Trenor, and stepfather Royce Clyde Zeigler II, found the note expressing remorse.

The couple are both charged with capital murder, accused of torturing Riley to death in a daylong discipline session designed to teach her proper manners. Prosecutors say Trenor and Zeigler beat Riley, pushed her head in a bathtub filled with cold water and ultimately threw her across a room, fracturing her skull.

Click here for photos of 'Baby Grace.'

Click here for photos from the trial.

Trenor, 20, is being tried this week. Zeigler will be tried later.

"My heart is black, dead. I can't live with myself without Riley," the note said in part.

Trenor's attorney, Tommy Stickler Jr., questioned Cazares about another document, this one found in a search of a storage unit that Trenor and Zeigler rented. It was a list of nine things that Riley needed to learn.

The list, called "Rules for Riley," included such things as "being polite," "behaves in public," "toys stay in her room" and "listen to mom & me." There was space for a 10th item on the list but it was left blank.

Cazares agreed, under questioning from Stickler, that investigators never would have found the list without Trenor's help.

After Riley was killed, the couple bought a plastic container, partially filled it with cement, stuffed her beaten body inside and stored it in a shed at their home before dumping the remains in Galveston Bay in September 2007, according to authorities.

Even though Zeigler is set to be tried later, he has been a constant figure in Trenor's trial.

Trenor, in a four-hour videotaped statement to police that was played in court earlier this week, admitted to participating in the daylong assault, but said the session was Zeigler's idea, and that it was he who threw the child across the room when he became frustrated that the discipline session wasn't working.

Zeigler's defense attorneys, who were in the courtroom on Wednesday, called Trenor's statement to police a "fantasy" and a "lie."

"The only person who is criminally responsible for the death of that child is Kimberly Trenor," said E. Dee McWilliams, one of Zeigler's attorneys.

McWilliams said Zeigler was not a witness to what caused Riley's death. But he declined to elaborate further, saying he wanted to let the prosecution present its case.

Trenor and Zeigler met playing an online video game and married in June 2007 after Trenor moved with her daughter from Mentor, Ohio, a suburb of Cleveland, to Spring, a suburb north of Houston.

Riley was dubbed "Baby Grace" while investigators worked to identify her decomposed remains.

The toddler's identity was a mystery for weeks until Riley's paternal grandmother in Ohio, Sheryl Sawyers, saw an artist's sketch of the girl and told authorities in Texas she thought it was her granddaughter.

The call from Sheryl Sawyers led authorities to Zeigler and Trenor. Investigators eventually discovered the couple had invented a story that Riley had been taken away by child welfare officials in Ohio.

Trenor could receive an automatic sentence of life in prison without parole if convicted of capital murder. The jury could also convict her of a lesser charge.

Prosecutors declined to seek the death penalty against either her or Zeigler, 25, because they didn't think they could prove that the pair would be a future danger, a requirement for such a punishment.

Trenor and Zeigler are being held in the Galveston County Jail under bonds of $850,000 each.