A mother accused of fatally beating her 2-year-old daughter fully participated in the discipline session that led to the toddler's death and never tried to stop it, a police investigator testified Wednesday.

Galveston County Sheriff's Sgt. Michael Barry told jurors that Kimberly Dawn Trenor whipped the toddler, Riley Ann Sawyers, with a belt and helped to repeatedly dunk her head in a bathtub of cold water. Riley died of three skull fractures she received when Trenor's husband, Royce Clyde Zeigler II, threw the child across the room, authorities said.

Trenor's lawyer has argued that the 20-year-old never intended to kill her daughter and that she was under the influence of her husband, who took the day off from work to have an all-day "discipline" session with Riley to teach her manners.

Click here for photos of 'Baby Grace.'

Click here for photos from the trial.

Barry testified that Trenor, in a long statement to police, never said she was forced to participate. But he also said Zeigler told investigators that Trenor was primarily responsible for Riley's death.

"I wasn't surprised by that," Barry said. "Each person is going to minimize their involvement. Each person is going to point the finger."

Wednesday morning's testimony was less gruesome than what the seven-woman, five-man jury heard on Tuesday, when the horrific details of the daylong discipline session came to light.

"It seemed like it went on and on," Trenor said in a more than four-hour videotaped statement she gave to police that was played during her capital murder trial. "I never meant for what happened to happen."

However, prosecutor Kayla Allen told jurors that Trenor and Zeigler are both responsible for her death when they tried to discipline Riley on July 25, 2007.

"You've got to know ... the result would be death from what they did to her," Allen said.

After Riley was killed, beaten so badly that Trenor said Zeigler complained of it making his shoulder sore, the couple bought a plastic container, partially filled it with cement, stuffed her beaten body inside and stored it in a shed. They tried to bury it in a wooded area north of their home, but when that failed, they dumped it in Galveston Bay in September. Riley was dubbed "Baby Grace" by investigators in October 2007 after they found her remains and worked to identify her.

But the container did not sink, she said. A fisherman found it on a tiny island about a mile from shore the next month.

At the defense table, Trenor teared up as she watched the videotape on a large screen. Several members of the jury of seven women and five men wiped away tears.

Trenor told police she and Riley moved from Mentor, Ohio, a suburb of Cleveland, to Spring, a suburb north of Houston, in June 2007 to be with Zeigler after she met him playing the online video game World of Warcraft.

Trenor said she and Zeigler fabricated a story that Riley had been taken away by officials with Child Protective Services in Ohio to explain her disappearance to relatives.

Trenor said Zeigler tried to commit suicide after Riley's death and wrote a note in which he said she was innocent "of the sins I committed."

The toddler's remains were unidentified for weeks until an Ohio woman named Sheryl Sawyers saw an artist's sketch of the girl, believed it was her granddaughter Riley and called authorities.

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. Zeigler will be tried later.