Produced by Lisa Freed and Gail Zimmerman[This story previously aired on July 30, 2011. It was updated on May 25, 2013.]
Linda and Jim Dulin are convinced that their daughter, Kari, was murdered by the man they once embraced as a son-in-law: Baptist preacher Matt Baker.
"Kari was a very good minister's wife. Faith was very important in her life," Linda Dulin told "48 Hours" correspondent Erin Moriarty. "This was a man who was capable of the ultimate evil."
Matt Baker has always claimed that his wife committed suicide, just as he told the 911 operator a little after midnight on April 8, 2006:
911 Operator: This is 911, do you have an emergency?
Matt Baker: Yes, I think my wife just committed suicide.
He said he went out to get a video and gas for his car. When he arrived home, Baker found his wife lifeless on the bed... an empty bottle of Unisom and a suicide note on the table.
"I -- felt to see if she was breathing. She was not. I shook her, she didn't answer," said Baker.
Their daughters, Kensi, 9, and Grace, 5, were asleep in nearby bedrooms.
Baker says it was because of another daughter, Kassidy, that Kari took her own life. He says she had never stopped grieving for Kassidy, who had a brain tumor and died seven years earlier.
"That was a tough time for her... every year," he told Moriarty. "It never got better for her."
But Kari's mother, and her family, did not believe that Kari would have abandoned her living children. The suicide note was typed -- even the signature. Linda Dulin grew more suspicious when she discovered that there were numerous phone calls between baker and a young parishioner named Vanessa Bulls.
"We talked a lot. But I talked to a lot of friends," Baker told Moriarty. When asked if he had an affair with Vanessa Bulls, he said, "Oh, no. I did not. There was never any relationship at all other than a friendship."
Matt Baker certainly didn't seem like he had anything to hide. He voluntarily spoke with the Hewitt Police a few months after Kari died.
"And so since then it has grown into a good friendship... and I know for a fact my in-laws don't like that," he told police.
And he wasn't shy about airing his grievances against the Dulins, who had been pushing the police to investigate their daughter's death.
"I think they're mad that they think I'm moving on -- I guess they think I'm moving on too quickly..." he told police.
Baker patiently answered every question they posed:
Hewitt Police: She was lying in the bed?
Matt Baker: Mm-hmm.
Hewitt Police: Was she clothed?
Matt Baker: She was not -- she had -- I'm trying to remember. No. She was naked.
The police also questioned Vanessa Bulls, who denied any affair with Baker:
Hewitt Police: Did you ever meet him romantically?
Vanessa Bulls: NO.
Hewitt Police: Never, OK.
And that, it seemed, was the end of the police investigation.
Linda Dulin was frustrated and felt that the only way she'd know what happened to Kari was to find out herself. So she hired attorney Bill Johnston and his team of investigators.
"We became convinced that he done it," Johnston told Moriarty. Investigator John Bennett added, "It seemed like every expert we talked to told us that it could not happen the way Matt Baker said it had."
Matt Baker said he was only gone for about 40 minutes, but Kari's body showed signs of lividity, the pooling of blood after death. The experts said it was unlikely that Kari could have ingested drugs, died and reached that state in such a short period of time. Moreover, records salvaged from Baker's workplace server were incriminating.
"We got to parts of it that showed he had search terms like 'overdose' and 'death by sleeping pills,'" said Johnson.
Johnston felt that police dropped the ball, but he was hamstrung. There was no autopsy and the death was classified as suicide.
"There was a guy who was holding a Bible on Sunday telling everybody how to live and he'd murdered his wife," Johnson said. "Every minute that went by, Baker was closer to getting away with it. And he knew it."
Johnston turned to Matt Cawthon, an old friend who was a member of the Texas Rangers -- the statewide law enforcement team. Cawthon agreed, unofficially, to help.
"The next step," Cawthon explained, "was to obtain records from telephones. Any other type of records that we might need."
To get those documents, Cawthon needed the district attorney's help, but was turned down flat. "I could not understand why I could not have the basic tools that I needed to continue with this," he said.
Cawthon persisted and finally convinced authorities to conduct an autopsy -- three months after Kari died. It was too late to test for drugs in her blood, but they did find Unisom in her muscle tissue, along with traces of Ambien, a drug Kari was not known to take. The manner of death was changed from suicide to undetermined.
In September 2007, a year-and-a-half after Kari died, the police now felt they had a homicide on their hands. Matt Baker was arrested and charged with murder. He was released on bond, thanks to powerhouse attorney Guy James Gray, who took the case pro bono.
"I only take the cases that I believe in with all my heart. And this is one of them," Gray told Moriarty.
And, Gray says, this is an injustice.
"You can't go forward with a murder case unless you can establish that it is a homicide. So, you have to establish cause of death," he explained. "And that, forensically, is just not possible in this case."