FREDERICK, Colo. — The mother of Christopher Watts, who has pleaded guilty to killing his pregnant wife and two children, said Monday she doesn’t believe her son killed his daughters.

Cindy Watts said she knows her son, Christopher Watts, is guilty of killing his wife Shanann Watts.

However, she does not believe he killed his two young children, Bella, 4, and Celeste, 3.

RELATED: Full coverage of the deaths of Shanann Watts and her daughters

“He did kill her, but the kids, no. It’s very difficult, very difficult. I can’t imagine my son doing that. He couldn’t have done that,” Watts said.

Cindy Watts spoke from her home in North Carolina. She said her family is not being allowed to speak to Christopher, who pleaded guilty earlier this month to avoid the death penalty.

“I want to stop it before it’s too late. I want to talk to him. I want to be able to talk to him. I love my son no matter what and I want to fight for him, and I don’t want him to go down for something he didn’t do,” Watts said.

Cindy Watts said she knows her son should spend a long time in prison for killing his wife, but she claims he was stuck in a verbally abusive relationship.

Christopher Watts pleaded guilty to nine charges: Five counts of first-degree murder, one count of unlawful termination of pregnancy, and three counts of tampering with a dead body.

He will be formally sentenced to life in prison without the possibility of parole on Nov. 19.

Shannan Watts’ family released a statement on Tuesday saying the comments by Cindy Watts were “vicious, grotesque and utterly false.”

According to an arrest affidavit, Christopher Watts was actively involved in an affair with one of his co-workers. He admitted to the affair at first, then denied it, according to prosecutors.

RELATED: Christopher Watts arrest affidavit

The arresting documents claim Watts caught his wife strangling their daughters to death after the couple had a conversation about them separating early in the morning of Aug. 13 in their Frederick home.

He claims he then strangled his wife “in a rage.” Watts told investigators he loaded the bodies into his work truck and buried them on property owned by his employer, Anadarko Petroleum.

Shanann Watts, who was 15 weeks pregnant, and her daughters were reported missing at 1:40 p.m. on Aug. 13.

The Colorado Bureau of Investigation issued a missing-endangered alert for the three the next day.

Christopher Watts said in a several interviews  that he didn’t know where his wife and daughters were.

The Frederick Police Department, the CBI and the FBI canvassed the area before arresting Christopher Watts on Aug. 15.

The body of Shanann Watts, 34, was recovered in a shallow grave near an oil tank.

Court documents said the girls were found in an oil well in close proximity to their mother’s body.

Court documents filed by defense lawyer James Merson said the girls had been submerged in crude oil for four days.