Daughter of murdered Lisa Knoefel describes her desperate attempt to save her mother

A woman has spoken out about how she witnessed her mother being stabbed to death by a 17 year-old girl her family was fostering, who was having an affair with her victim's 42 year-old husband. 

Megan Zanella, whose mother Lisa Knoefel was knifed 200 times by Sabrina Zunich in November 2012, told HLN's Sex & Murder about her mom's horrific final moments.

Knoefel, who worked as a social worker, was killed at her home in Willoughby Hills, Ohio, after Zunich began sleeping with Knoefel's husband Kevin. 

Kevin told Zunich he'd kill himself if she didn't kill his wife. 

Zanella told HLN: 'I was hearing screaming. I was also hearing the dog barking and I was like, 'What the hell is going on downstairs?

'So I walked down there and Brina is stabbing my mother to death and immediately I stay, 'Stop get off of her! 

'I was actually on top of her at one point and she shoved me. I immediately go into the office and call 911 and say, "'My sister is stabbing my mother to death. She is going to die.'" 

Megan Zanella was only 13-years-old at the time when her 41-year-old mother was stabbed nearly 200 times in front of her. She recounts how she rushed to call 911 screaming to the operator: 'My sister is stabbing my mother to death. She is going to die'

Lisa Knoefel was stabbed nearly 200 times by Sabrina Zunich in Willoughby Hills in November 2012 after she found out the then-17 year old was having an affair with her husband, Kevin Knoefel 

During the trial, Sabrina Zunich, 19,  said she had fallen in love with her foster father and feared he would commit suicide if she didn't carry out their plot to kill his wife

Zanella, who told HLN that she still has trouble sleeping at night, also claimed that a month before her mother's murder, Zunich had threatened her in their home. 

'She actually pointed a knife at me when we were in the kitchen and I knew it was all downhill by then,' she said.  

Zunich pleaded guilty to aggravated murder in 2014. She was sentenced to life in prison with a chance for parole in 30 years. 

Kevin Knoefel, who was 42 at the time of the murder, received the same sentence as the foster daughter after a jury found him guilty of conspiracy to commit aggravated murder and sexual battery.  

During Kevin Knoefel's trial, Zunich testified that he'd threatened to kill himself if she did not murder his wife. 

Lisa Knoefel was a social worker for the Cuyahoga County Department of Children and Family Services and worked in the sex abuse department, and Kevin worked as a truck driver.  

When Sabrina Zunich was 16, she was placed with the couple. Not long after, she and Kevin Knoefel started a sexual relationship, and discussed several plans to kill Lisa Knoefel, including shooting her and making it look like a burglary, or finding a hit man.

Zunich said she was manipulated into carrying out the murder, and was reassured by Kevin Knoefel that she would only do 25 years in prison if she was caught.

 Zunich stabbed and cut Lisa Knoefel more than 150 times with a 10-inch serrated knife after putting on a ski mask and attacking her in the bedroom 

Lisa Knoefel, 41, worked as a social worker in Ohio and took Zunich into her home when she was just 16 years old. She found out a year later that Zunich had been having an affair with her husband 

Zunich testified during her trial that on the night of the murder, she put on a ski mask and fatally stabbed 41-year-old Lisa Knoefel in her bed as she fought back. 

Zunich stabbed and cut her more than 150 times with a 10-inch serrated knife.

She was not deterred even though Lisa Knoefel fought and pleaded for her to stop and Zanella tried to pull Zunich off her mother and called 911.

Prosecutors have said they were unaware of Zunich's sexual relationship with Kevin Knoefel or that he had persuaded her to kill Lisa Knoefel until Zunich spoke with them in May, 2013 - six months after the murder. 

During the trial, prosecutors said Knoefel wanted his wife dead to collect $750,000 in life insurance. He also wanted his wife out of the picture but was afraid he'd lose custody of their three-year-old daughter if they divorced.

He told Zunich they could raise his daughter together.

In 2012, Sabrina Zunich (right), who was 19 at the time, killed her foster mother. Her foster father, Kevin Knoefel, 44, (left) was more than 20 years her senior, told her to do it. The pair were romantically involved 

At the sentencing, Judge Richard Collins said: 'I don't think there was any question she was manipulated and used by the co-defendant.'

But he said the seriousness of the crime outweighed all factors.

'Aggravated murder is aggravated murder,' Collins said. 'But this was not a single violent act.'

He said Lisa Knoefel suffered before she died.

'She was screaming for help and begging the defendant to stop. She did not die immediately. I cannot imagine the nature of terror and fear.'

At the sentencing Sabrina said she was remorseful.

'I want to say how sorry I am for all those I hurt,' she said. 'Lisa did not deserve what happened to her. I ask forgiveness be given to me - not for my benefit but for those who need the healing process to begin. I can't explain how much remorse I have and how much sadness I deal with.'

In Sunday's upcoming episode, one of the detectives is seen saying: 'This was definitely the worse crime scene I have ever scene in my career.'

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