The daughter of a woman whose body was dumped in an overgrown lot two years ago took part in the killing along with her boyfriend, a convicted sex offender, Houston police said.

The partially clad body of Undra Williams, 39, was found June 2009 in the 5000 block of Briscoe, in southeast Houston.

An autopsy later revealed that she had been stabbed to death.

On Friday, Houston police homicide detectives said Ejjetta Williams, the victim's daughter who had just turned 17 at the time, had masterminded the slaying.

"Nobody ever wants to believe that a child would kill their own parent," said Sgt. Ora Chandler, with HPD's homicide division.

The primary motive was the daughter's relationship with James Bishop, 31, who had already served a two-year prison sentence for sexually assaulting an 11-year-old girl, officers said.

"It is the ultimate crime when a child participates in the murder of their own parent," said Clarence Walker, who had known the victim since she was a child.

Confronted boyfriend

Undra Williams didn't want her underage daughter to associate with a registered sex offender.

She confronted him in March 2009 after he was seen leaving her home through a window with his pants down.

"He (Bishop) knew that would cause him a lot of turmoil," Chandler said. "I think that was the beginning of the end for her (Undra Williams.)"

Ejjetta Williams was not merely an innocent girl who had been manipulated by an older man, police said Friday.

"I believe (she) was as much responsible for the death of her mother as Bishop," Chandler said.

HPD detectives found several journals where they said Ejjetta Williams fantasized in graphic detail about her mother's death.

"She had the mind-set of plotting her mother's murder before she ever met Bishop," Chandler said.

Blamed stepfather

After her mother's body was discovered, Ejjetta Williams tried to implicate her stepfather in the killing. Chandler said he was found to be innocent of any involvement.

"She later said she made the story up," Chandler said. "It's a very, very sad situation."

In February 2011, Bishop was charged with sexual assault of a child stemming from his past relationship with the then-underage Ejjetta Williams.

Detectives wanted to give her the opportunity to talk about her mother's death with him securely behind bars.

"She was considered to be a suspect but we wanted to give her the benefit of the doubt," Chandler said.

Bishop and Ejjetta Williams continued their relationship ever after her mother's slaying.

The two were charged with murder and are in the Harris County Jail, officials said.

On Friday, other family members of Undra Williams could not be reached for comment.

mike.glenn@chron.com