What happened to Lena Chapin? And where is Sandra Klemp now? All the theories behind the Unsolved Mysteries case

So what exactly happened to Lena? Has she ever been found? And where is her mother Sandy Klemp now?

Here's everything you need to know about the case, including theories from newly release footage which didn't make the documentary.

Who is Lena Chapin?

Lena Chapin, also known as Liehnia May Chapin, disappeared in 2006 in Dent County, Missouri, three years after making the shocking allegation that she helped her mother, Sandra Klemp, kill her stepfather and her mother's third husband, Gary McCullough in 1999.

As chronicled in the show, Lena alleged in a tape that her mother killed her husband and made her get rid of the body.

The entertainment news website Meaww reported that Chapin confessed to Gary's brother Albert in 2003, three years after he went missing.

According to an account that she gave Albert: “He was sitting on the couch, eating scrambled eggs. She walked out and shot him three times in the head. Two, maybe three times… and she couldn’t hack it until we got home. And she wrapped him up with plastic stuff and hay strings… she dragged him to the bedroom. She locked the door and we got home. Mom made me stay in the bedroom. She didn’t want me to see him. But I’d already seen him. ‘Cause I looked through the door. I didn’t believe it and I wanted to see.”

Lena then went on to describe how they pulled up carpets and bleached the floors in an effort to get rid of any evidence.

Albert recorded Lena's allegation at the time when she was 17-years-old, and the Salem News reprinted it in an article, although she later went back on this.

However, in 2013, when Judge Carr Woods heard the wrongful death lawsuit brought against Sandy and her fourth husband, Kris Klemp, Lena’s tape was not allowed to be used as evidence.

Sandy hasn't commented on the Netflix documentary.

While none of Sandy's daughters except Lena have ever claimed their mother killed Gary, Lena's sister Robin Shoemake said that she remembers her mother and Kris Klemp (Sandy's fourth husband) carrying Gary's body out of the house on the night of May 11, 1999 — the day he disappeared.

She said: "That night mom told Lena to make sure that none of us came out of the bedroom. Lena had fallen asleep in front of the door. And even as young as I was, I still remember something wasn't right. And in our room, there was a window and I see mom and Kris struggling, trying to pull something big. I mean it was Gary no doubt but he was wrapped up in something. I mean you could see the boots that he had on. It scared me."

What happened to Lena Chapin?

In 2006, Lena went missing not long after she was issued a subpoena to testify in court following the claims she'd made against her mother.

Her sister Robin went looking for her at her apartment in Missouri and was greeted by her then boyfriend Jason, who said that her mother Sandy had told him Lena had moved to Florida with another man.

Her sister wasn't convinced, and says that when she learned her mother was with Lena's baby son Colter, she knew her mother had done something.

Sandy has never been formally charged in connection to Chapin's case. She and Kris Klemp, who she married shortly after Gary's disappearance, were found liable for his death in a lawsuit filed by his children.

They were ordered to pay $7 million, but the family claims in Unsolved Mysteries that they haven't received any of the money.

Lena's case has gone unsolved, and her and Gary's bodies have never been found.

What are the latest theories surrounding Lena's disappearance?

Since the documentary dropped on Netflix, amateur detectives have been inspired everywhere, with fans looking into clues and coming up with theories of their own.

Recently, Netflix released files of unseen interviews and pictures on each case, which didn't make the documentary.

In Lena Chapin's document, which was posted to the streaming site's Reddit page, an unseen clip shows her description of the night Gary was allegedly murdered to hold many inconsistencies.

Investigator Brian Martin noted problems with Chapin’s story of taking a ride in Gary's truck before he died, saying: “Something that was interesting when he did find Gary’s truck was there was one place to sit and that was the driver’s seat. You could sit on the passenger side, but you couldn’t put your feet on the floor as there was so much litter,” he says in the new footage."

He continued: “I found it ironic because in the one interview I did get with Lena, she said that on the night Gary left she rode with him in the truck but didn’t want to be seen with him. And she sat on the floor of the truck. I commented to the other investigators that were there: ‘nobody has sat on that floor for a long time.’”

As well as this, the clips revealed new claims against Kris Klemp.

According to Martin, Jennifer Klemp - Kris Klemp's wife at the time of Gary's disappearance - delivered a damning account of her husband’s behaviour.

"She said they were having a screaming match and he said something to the effect of ‘I can’t worry about this stuff right now. I’ve got to worry about killing a man.," he recalled.

Retired Sheriff Mick Epperly added: “Jennifer told us she took Kris Klemp to the location of the Gary McCullough­ place. Dropped him off on the curb. And later picked him up that night. And Jennifer said Kris was as scared as he could be.I believe that was probably the night Gary was burned.”

Who is Sandy Klemp? Where is she today?

Two of Sandy's daughters, Brandi Petersen and Robin Shoemake, and one of her ex-husbands have discussed Sandy in detail in the documentary.

Brandi said that although they saw pretty hard times growing up, Sandy always made sure that they had food on their plates.

"My mom was a good mom growing up," she said. "She was very straight-laced. Never done a drug, smoked a cigarette, alcohol, nothing. My whole life. She just wasn't like that. She would always tell us, every single night, 'God bless you and love you'. Every night. That's the mom I remember and I miss that mom so much. But... what can you do?"

She added that her mother was not one to settle down with a guy for life, saying; "She used her sex appeal a lot and that's a lot of the reason why men gravitate toward her. And she never did stay with one particular man for more than two years. And she always went after the married ones or one that had brothers."

Before Sandy married Gary McCullough, she was married to his brother Albert for a few years.

Speaking in the documentary, Albert said: "When I was married to Sandy, the first two or three years wasn't too bad but then she got to fooling around and I didn't know who it was and it ended up being Gary. My brother. Me and him had a little fistfight down there on the ridge and he beat the tar out of me and I beat the tar out of him."

Sandy's relationship with Gary didn't last however, as she'd reportedly started an affair with Kris months before Gary disappeared.

Prior to his disappearance, Gary's friend Jeff Allen said that Sandy tried to kill Gary with a gun. Luckily, the firearm did not go off when she tried to shoot. By that time, Gary had allegedly become aware of his wife's affair and was planning to file for divorce.

Gary then went missing, but Sandy didn't report it until two days after when some deputies had shown up at their ranch for a cattle call.

After Lena's disappearance, Sandy adopted her son Colter as her own.

According to the Monnet Times, she and Kris got divorced in 2014. Sandy has since remarried a man named Joe Wink and is now known as as Sandy Wink. The two live in Mount Vernon, Missouri with Colter.

What are the alleged motives behind Lena Chapin's disappearance?

Detective Rick Letchworth, who investigated Lena's disappearance said in the documentary that he believed that there were two primary reasons behind Sandy's alleged involvement in it.

"Based on my interviews with Brandi and Robin, I believe Sandy had two motives for making Lena disappear," he said. "Lena helped make Gary disappear. She had first-hand knowledge of what happened. And if Lena talked, what that could potentially do. Also, Lena had a son, Colter, that Sandy desperately wanted. So much that Sandy would, by accounts, make him call her 'mom'."

Unsolved Mysteries is available to stream on Netflix. Check out our lists of the best TV shows on Netflix and the best movies on Netflix, or see what else is on with our TV Guide.