In an explosive interview with HLN’s "Nancy Grace" show, the ex-fiancee of "Making a Murderer" subject Steven Avery called him a "monster" behind closed doors and said the documentary series sweeping the nation is "all lies."

"The first thing I’m going to ask you is, do you believe Steven Avery killed Teresa Halbach?" Nancy Grace’s senior producer Natisha Lance asked Avery's former fiancee, Jodi Stachowski.

"Yes, I do," Stachowski said.

"Why?" Lance asked.

"He threatened to kill me, and my family and a friend of mine," Stachowski replied.

Avery hurtled into the spotlight when the series debuted on Netflix last month. "Making a Murderer" chronicles Avery's 18 years in prison for a rape he didn't commit and his subsequent arrest on murder charges in a separate case.

He was convicted in 2007 of killing Teresa Halbach, a 25-year-old photographer for "Auto Trader" magazine who vanished while taking photographs of a van at the Avery family's salvage yard in Manitowoc County, Wisconsin.

Her charred remains were found in a burn pit in Avery's yard. The defense argued in court the bones had been moved and Avery framed.

In her first interview since the series' release, Stachowski said the man portrayed in "Making a Murderer" is nothing like the reality she endured on a daily basis during their allegedly violent, volatile and abusive two-year relationship.

"He’d beat me all the time, punch me, throw me against the wall," she told "Nancy Grace."

Stachowski said the abuse got so bad, she purposely ingested rat poison on two occasions so she would be hospitalized to "get away from him."

Avery's attorney, Kathleen Zellner, did not immediately return phone and email requests for comment Thursday.

At one point in their relationship, Stachowski claimed, she was in a bathtub and Avery threatened to throw a blow-dryer into the water, allegedly telling her "he’d be able to get away with it."

"He’s sick," Stachowski reasoned.

On the occasions when she tried to leave Avery, Stachowski said he would do things like smash the windshield of her car so she couldn’t drive.

She said Avery was jealous and controlling, to the point of following her to work and spying on her through the windows on a regular basis. If he saw something he didn’t like, she told "Nancy Grace," he would hit her hard enough to leave red marks on her body.

Stachowski said there were only a total of "maybe two" times when Avery was not abusive toward her. After one particularly violent night when Stachowski says she was hit and choked, she finally called the police, but Avery "dragged her out the door" so they could get out before the cops arrived.

Stachowski hasn’t seen the hit Netflix documentary, she says, and doesn’t want to. Stachowski said in the interview she went as far as asking the filmmakers not to include her in the series "because it’s all lies."

The documentary's creators were never made aware of the issues that allegedly consumed their relationship when the camera crews weren't around, according to Stachowski.

Many who watched the gripping 10-part series saw Avery's then-fiancee passionately stand by Avery’s innocence, even supplying her phone records to prove the couple had "normal" conversations during the time when Avery allegedly killed Teresa Halbach.

Recalling those phone calls now, Stachowski says, "he did sound funny … like he was lying or hiding something."

Stachowski claimed during the one-on-one she was strong-armed into "saying nice things" about Avery and that Avery had told her how to act, what to say about him and to "smile and be happy," otherwise she "would pay."

"I didn’t know what to do," she said in the interview. "I didn’t want to get hurt ... He told me once if I did leave him he’d burn my mom’s house with them and my daughter in it."

Talk of Halbach's brutal murder is only time during the interview when Stachowski is overcome by emotion, saying she went through months of intense counseling because of the guilt she carries over being in jail on the day of Halbach's death.

"They tell me, 'It’s not your fault,'" she cried. "But if I would have been there, she still would have been alive."

Stachowski said she asked Avery multiple times if he killed Halbach, and each time he adamantly denied it — a denial she says she doesn’t believe.

"He told me once … 'All b---- owe him' because of the one that sent him to prison the first time," Stachowski said.

Stachowski told "Nancy Grace" she believes Avery's young nephew Brendan Dassey is innocent, but was likely scared for his life and felt threatened by his uncle. Dassey was 16 at the time of the crime and is also serving a prison sentence on a murder conviction.

When asked if she had seen Avery physically hurt others before, Stachowski said, "No, but Steven’s one person I don’t trust."

"He’s like Dr. Jekyll and Mr. Hyde," Stachowski said, describing Avery as a sometimes "semi-nice person, and then behind closed doors he’s a monster."

Nancy Grace has been outspoken in her personal belief that Avery is guilty of Halbach’s murder, even claiming that Avery once "told her to her face" he was in the burn pit where prosecutors say bones from her remains were recovered.

On Monday, Avery filed an official appeal of his conviction.