Investigators use an unlikely clue to bring young mom's killer to justice

This story originally aired on Dec. 10, 2022. It was updated on July 29, 2023.

On Oct. 15, 2019, Joseph Elledge walked into the Columbia, Missouri Police Department without a lawyer to tell detectives about the mysterious disappearance of his 28-year-old wife, Mengqi Ji — six days earlier.

JOE ELLEDGE (police interview): We didn't have any big fights ... I think the last big fight was actually the week before. And it wasn't really a big fight.

The 23-year-old described his wife as tense and withdrawn the night before she disappeared, so he gave her a massage.

JOE ELLEDGE (police interview): I was going kinda slow. I was trying to drag it out because I wanted to extend the amount of time that we were together doing something.

According to Joe, Mengqi eventually went to sleep, saying she had to be somewhere in the morning.

JOE ELLEDGE: I asked her about three times, "Who is she meeting?" And her answer was just, quote, "Me." ... she wouldn't tell me who she was meeting or where she was going, what she was doing.

The next morning, Joe says he woke up alone. His wife was gone.

Dan Knight: He was claiming ... she had just disappeared — that she had left her little girl behind. Her phone was left behind ... her car. Her car keys were left behind.

From the beginning, then-Boone County prosecuting attorney Dan Knight, had doubts about Joe's story.

Dan Knight: We were trying our best to leave no stones unturned. But there were a lot of stones.

Joe told investigators that after his wife disappeared, he found journal entries on her computer where she'd written about an online emotional affair she was having with a man living in China.

JOE ELLEDGE (police interview): The last paragraph said ... "like It's sad though that I have no interest in my husband."

The day Joe spoke with detectives, he also did an exclusive interview with local CBS affiliate, KRCG, and implied that his wife may have left him for another man.

JOE ELLEDGE (KRCG interview): I hope that she's with - at least with somebody who - who cares for her, you know, enough to keep her safe.

Joe and his family hired attorney Scott Rosenblum, who points out there were intimate texts between Mengqi Ji and the man she was communicating with.

Peter Van Sant: Sexual in nature?

Scott Rosenblum: Very sexual.

Texts like this one where she wrote, "I want you so much right now." 

Peter Van Sant: And did she ever express love for him in any of these communications?

Scott Rosenblum: She did.

The question was, had Mengqi run off to be with that man who lived in China, where she was born?

Amy Salladay is the Ji family's attorney.

Amy Salladay: Mengqi was born during China's One-Child Policy. But Ke Ren, Mengqi's mother, would say that "We only ever wanted one child. We wanted to give all of our love to this child."

Yáo Li: Mengqi is like the — the kid all the parents would want.

Yáo Li is a Chinese immigrant, and an assistant prosecutor in Boone County, who helped Dan Knight communicate with Mengqi's parents.

Yáo Li: They are really, really proud of her. ... I know how hard it is to get into a top university in Shanghai and Beijing ... the competition ... is really intense. ...  And she did that.

Dan Knight: Then she came to the University of Missouri in 2012 where she finished up her undergraduate studies and then she also obtained her master's degree in mechanical and aerospace engineering.

Peter Van Sant: This was a brilliant woman. Correct?

Dan Knight: Absolutely.

One of her professors hired her right out of school at his biomaterials company, "Nanova," where Joe also worked.

Dan Knight: Joe ... grew up in Kansas City. ... he then came to the University of Missouri, and he studied engineering, and he met Mengqi at Nanova Biomaterials. ... My understanding is, is that she was his supervisor.

The two quickly fell in love, and a year and seven months into their relationship, Joe proposed. He took a knee on a trail in Rock Bridge Memorial State Park called "The Devil's Icebox."  Two weeks later, they were married.

Dan Knight: I believe there was a rush to get married because Mengqi's visa was about ready to expire.

Yáo Li: It's a really foreign concept for American citizens to understand the stress that a immigrant is facing ... She's fully capable to support herself financially. But she cannot get this green card. ... So, this really changes the power dynamics of a marriage.

Nearly five months into the marriage, Mengqi was offered a big job.

Yáo Li: And then she found out that she's pregnant.

Mengqi and Joe decided she should turn down the job to be a full-time mom - even though, at the time, she was the sole income earner. Joe had quit working to finish school. In October 2018, the baby was born.

Yáo Li: So that's the dynamic of this marriage. Mengqi was completely isolated from all the support system that she can have. ... the little baby's the only thing she has.

Her one lifeline was a daily call with her mother in China. It was their ritual. So, when Mengqi didn't call on Oct. 9, 2019, her parents sent a friend living nearby to check on her.

JOE ELLEDGE (police interview): You know, I told him everything that happened. I told him that she just hasn't been here for a couple days.

And it was only after that visit — the day after he said his wife vanished — that a seemingly unconcerned Joe Elledge finally called police to report her missing.

JOE ELLEDGE (to 311): Hi. I need to file a missing person's report.

He didn't dial 911 - Joe called the non-emergency 311.

Peter Van Sant: Do you find that suspicious?

Dan Knight: Absolutely. Absolutely. ... it would be natural for him to have reported this immediately.

Instead, Joe would tell police that the day he woke up and found his wife missing, he went on two long leisurely drives in her car-with their baby in the backseat-looking for new hiking trails.

JOE ELLEDGE (police interview): There's this, there's just this big area that's all - that's all green on the Google Maps. And so, I wanted to go and see if there were walking paths back there.

Naturally, that raised eyebrows.

DET. JON VOSS: Did you lock your door when you left the apartment?

JOE ELLEDGE: Yeah.

DET. JON VOSS: If she comes home, how is she gonna get back in? You've got her keys and her car. Her phone's in the house. She can't even call anybody.

JOE ELLEDGE: Yeah, I don't know.

Detectives, and Dan Knight, suspected foul play. But there was no physical evidence: no blood, no weapon, no witnesses, no body. There was also no evidence that Mengqi took off with that man in China.

Dan Knight: And then also — it became — apparent early on that Mengqi would not have abandoned her child, her 1-year-old daughter. ... She was a great mother.

During his interview with detectives, Joe gave them access to his phone — and on it they found something stunning: 10 hours of secretly recorded conversations with his wife, like this one:

JOE ELLEDGE (audio recording): I would like to discuss our relationship. And I am kinda ready to discuss the end of it as well.

Dan Knight: Joe told Mengqi ... that he wanted to divorce her.

JOE ELLEDGE (audio recording): I don't like being married (laughs) to you. I don't like living with you. ... It's been a terrible relationship. I'm eager - to end it.

Dan Knight: He was asking her whether or not she was going to basically cooperate ... And if not ... was going to - he was going to tell the judge ... "that she had been abusive to him."

JOE ELLEDGE (audio recording): Should I mention in court that you're abusive to me? Should I ask them to-deport you?"

But that was nothing, says Dan Knight, compared to the nearly four-and-a-half hours of secretly recorded audio they found on Mengqi's phone.

Peter Van Sant: What was on those conversations of significance?

Dan Knight: Unvarnished Joe Elledge.

JOE ELLEDGE (audio recording): If you keep acting this way, I've told you before, ain't gonna be pretty.

A CONTROLLING RELATIONSHIP

JOE ELLEDGE (audio recording): What are you trying to do? ... Are you trying to make me go crazy so that you can call the police on me and take my f*****' baby away from me?

It was Oct. 29, 2018, about a year before Mengqi Ji would disappear, when she secretly recorded her husband Joe, going ballistic, for nearly an hour.

JOE ELLEDGE (audio recording): Do you want me to f