(CNN) -- Former Sunday School teacher Melissa Huckaby apologized Monday in a California courtroom after being sentenced to life in prison without parole for killing her daughter's 8-year-old playmate.
"It is not enough to say that I'm sorry, but that is all I can do," a tearful Huckaby told a hushed courtroom about the death of Sandra Cantu, whose body was found in a suitcase in a pond on a dairy farm 10 days after she disappeared in Tracy, California, in March 2009.
"From the day Sandra has died, I've had to live with the consequences of what I have done," said the tearful 29-year-old woman as she daubed her eyes and blew her nose. "For the rest of my life, I am going to have to live with these feelings of responsibility for her death. Not a day, not an hour goes by that I don't think about her."
She added, "I loved Sandra a great deal. She was a sweet, innocent little girl who did not deserve to have such a short life. I alone am responsible for Sandra's death."
Dressed in a red prison jumpsuit and seated next to her lawyer, Huckaby directed comments to the victim's family. "I know that I have caused you a great deal of grief, and for that I am truly sorry," she said. "I should not have taken Sandra from you, and I want you to know she did not suffer and I did not sexually molest your daughter."
Huckaby also apologized to her own family -- including "my own daughter, whom I have lost" -- and thanked them for their support.
"I wish I could give you an explanation," she said. "I still cannot understand why I did what I did. Every day, I try to discover my motivation, but I still do not have an answer. This is a question I will struggle with for the rest of my life."
In a plea deal that removed the possibility of the death penalty, Huckaby admitted to the special circumstance of murder during the course of a kidnapping, which translates into life without parole. She has 60 days to appeal.
Prosecutors had charged Huckaby with murder, kidnapping, lewd and lascivious acts on a child under 14, and rape by instrument.
San Joaquin County Superior Court Judge Linda Lofthus lifted a gag order and said she would consider unsealing documents related to the case.