(CBS) NEW YORK -- A Texas man charged with murdering his ex-girlfriend, told a producer for the "Dr. Phil" show that he killed Michelle Warner on the night of Sept. 22 and buried her body in a shallow grave eight hours from their Houston home.
"She took a swing at me and I grabbed her," says Mark Castellano, 37, calmly on a tape played on Thursday's "Dr. Phil" show. "Her neck popped."
Castellano went on to say that he wrapped Warner's body in a blanket, wrapped her head in a plastic bag, and put her body in a closet before he packed up the car and drove the couple's 3- year-old son to his parent's home eight hours away in Odessa, Texas.
Castellano also says that the little boy was home at the time of the murder and saw his mother's body.
"He saw her foot sticking out," says Castellano. "I said, 'Mommy's sleeping.'"
Castellano has been charged with murder and according to the Houston Chronicle, his bail was set at $50,000.
Before confessing, Castellano taped a sit-down interview with Dr. Phil McGraw where he denied hurting Warner and claimed to have no knowledge of her whereabouts. In the interview, Castellano described the couple's tumultuous relationship, admitting that he had choked Warner during arguments in the past. He also accused her of kicking and punching him, and abusing prescription drugs.
"She hits me all the time and I don't retaliate," said Castellano. "She walked all over me, she just owned me. I didn't hurt her at all."
Castellano spun a tale to McGraw about the night of Sept. 22, 2012, saying he and Warner had fought, that she'd been taking Xanax, and that she went into their bedroom, slammed the door and then disappeared, leaving her car behind. When McGraw asked how she could leave without her car, Castellano answered that she must have called someone to pick her up.
"She's always carrying narcotics and she's definitely, definitely afraid of being pulled over by the police," said Castellano.
McGraw pointed out that her cell phone hadn't been used and Castellano said that Warner "has a bag of cell phones...she probably had at least 11 of them."
According to the Houston Chronicle, Warner was a paralegal who had had appeared in court in 2003 for misdemeanor theft and 2006 for possession of a small amount of cocaine.
Warner's mother, brother and sister-in-law learned that her body had been found after landing in Los Angeles to film a segment for the Dr. Phil show. When McGraw played the tape of Castellano's confession to the family, none seemed shocked. They said they had suspected it all along.