Transcript for Fiancé of slain Texas mom on finding out his wife’s friend is suspected of kidnapping
Reporter: A holiday season in Austin. Made sweeter by the birth of a baby girl. Heidi Broussard welcoming her you new baby. Everybody was coming over. It was amazing. Reporter: The best friend there in T delivery room. Megan came down. She was the first one down. And she was there the whole entire time. Reporter: Megan, just weeks away from delivering her own baby. They were planning to try to have the baby on the same day and all this. And they were excited together. Meagan and Heidi. Reporter: But authorities say Megan never had her baby. That she faked the whole pregnancy and carried out the ultimate betrayal. The desperate search for a missing mother. She took her child to school and just vanished. That Texas mother had just given birth. Reporter: Megan accused of kidnapping baby Margo. Her best friend found strangled to death but no one yet charged with the murder. Makes me angry. These beautiful kids don't deserve this. She didn't deserve this. Reporter: Magnetic and spontaneous is how he describes his 33ear-old fiance, Heidi Broussard. She loved music. Anything you brought up, she could always talk about. And her laugh and her smile were so contagious. Reporter: December 12th started like any other day. Shane leaves for work while Heidi drops their young son off at school. But when Shane returns home that afternoon no sign of Heidi or the newborn. I just got home and nobody was there. Reporter: Hours go by and he begins to panic. Shane calls his father Ty. He says something's not right, dad, she's not here, and then he started noticing nothing was missing, nothing to take care of Margo. Reporter: And you knew wasn't volunteery. No. If you know Margo, she would not leave like this. She'd tell a friend. Reporter: Shane turning to family and friends for support, including Megan, Heidi's best friend. They'd met years earlier at a bible school. I was like, have you heard from her? She's like no. She started crying on the phone. Like where is Heidi. And, yeah, she played it off. So well. Reporter: Even as he pleaded to news cameras for help, some were skeptical about Shane. I just want her safe. Statistically, it's almost always the fiance, the husband, the boyfriend, the man in the woman's life. Not this time. Reporter: Instead, it was the best friend police focussed on. After investigators started talking to people close to Heidi, they say Meagan's story wasn't adding up. She claimed to have given birth December 12th, the same day they the gray Nissan was at the and the complex the day they disappeared and they saw a woman carrying a small infant being helped into the rear of a vehicle by a front seat passenger who they later identified as Megan in a lineup. Megan's cell phone was also pinged in that area at the same time that Heidi goes missing. Cell phone pings don't lie. Reporter: Investigators also say they dug into her internet search history. There are nearly 200 searches for the name Heidi Broussard in the days surrounding Heidi's disappearance. On the day that Heidi disappears, along with baby Margo, on the same account, on the same device, we believe, there is a search around 10:31 P.M. That day, that asks for hits on reason for an amber alert. Here's the kicker. At that time, no amber alert had been issued. Reporter: A week later in Houston, authorities track down Megan's former boyfriend. The two were still living to the at this house. They find them in the grocery store buying baby formula forehis new baby girl. And they show him a flier, a flier with baby Margo's photo on it. He takes one look at this flyer and says that's baby at my house. Reporter: Police had already been surveilling the house, finally going inside, and then a shocking discovery. I got a phone call at two-something in the morning. I started crying, and my dad tried to calm me down. And I laid down on the kitchen floor. That's all I remember. We did recover an infant, female child that we do believe at this time is Margo. However, we are awaiting the results of DNA testing to confirm that identity. Reporter: Outside, a grisly find. Heidi's strangled body in the trunk of Megan's car. I still don't believe it. For some reason, I'm like, it's still not, it's processing, but it's not sing. Cause she was a friend. I don't know what brings somebody to do this sort of thing. But it's just the worst of the worst. Reporter: Megan charged with two counts of kidnapping and one count of tampering with evidence, but she hasn't been charged with murder at this point. Her defense team maintaining their innocence, writing that they are anxious to review the evidence collected thus far. I know you want justice, how do you feel knowing at this time that no one's been charged with her murder? I don't understand this at all. Police could be waiting for all the facts and evidence before they make a murder charge. Reporter: Do you believe Megan's responsible? I believe so. Or somebody talked her into it. Heidi is so strong. There's no way Megan could have took her down by herself. I'm going to miss you Reporter: Last month, family and friends grieving at a vigil for Heidi. I'm really going to miss her voice. Reporter: Shane laying his fiance to rest two days after I want her to be recognized for the person that she was the best mom in the entire world. I got to be the best dad ever. Reporter: Shane is determined to make sure Heidi's memory lives on. Shane, when Margo grows up, what will you want her to know about her mother? Just that her mom would love her. She still does. Reporter: For "Nightline," I'm Kaylee Hartung in Austin, Texas.
This transcript has been automatically generated and may not be 100% accurate.