HOUSTON (CBSDFW.COM) - Eric Williams grew up in Azle.
A boy scout. In the band. He graduated from Texas Christian University where he was in the Reserves Officers' Training Corps (ROTC).
Kim Williams was raised in Dallas.
She graduated from Skyline High School. Her friends called her a "Barbie." She did college course work at the Southern Methodist University and the University of Texas at Arlington.
Eric and Kim met in the late 90s and married on May 13, 1998.
Fifteen years later, the Williams' thrust themselves into the national spotlight after committing what true crimes writer Kathryn Casey calls, "one of the three most notorious murders of the century."
"You don't kill prosecutors and prosecutors' wives. This is something we hear happening in other countries but not the U.S.," said Casey.
Eric and Kim Williams have turned down every interview request except Casey's. They independently agreed to interviews from prison with her after she told them she was writing a book called, "In Plain Sight."
"You know Eric was actually very pleasant to talk to. He has a really good sense of humor."
When the CBS 11 I-Team asked if he showed remorse, Casey said, "No, Eric remained steadfast that he didn't kill anyone."
But Casey says in Kim tells a very different story.
Casey says Kim told her Eric's plan began right after Kaufman County convicted him for stealing $600 worth of computers, a move caught on surveillance cameras.
She said Williams created a hit list to take revenge on those who he says ruined their lives.
"He came home and told her Mark Hasse would be first, and he had it planned and he started talking about Tombstone." In the movie, Tombstone, she said, "The main gun battle happens off the main square. ...he showed up that day, Eric did, dressed all in black just like the character in that movie."
As suspicions rose about the Williams' and their possible connection to Hasse's murder, Casey says Kim told her that Eric "loved the news coverage. Kim said he was on his TV and computer all the time watching the news coverage."
Eventually growing paranoid that detectives had bugged his house, Kim says he did something rather unusual with her and a deck of cards. "He would haul her into the pantry and hold up the king for Mike and the queen for the judge and they would argue back and forth over who he would kill next."
On March 30, 2013, dressed "in costume" again, Eric gunned down District Attorney Mike McLelland and his wife, Cynthia, in their home.
From behind bars, and to this day, Casey says Eric would never admit to the murders. "He would say that never happened or I didn't kill those people. He never admitted any of it."
In early 2013, during the murders, Kim was sick and says Eric kept her so high on liquid morphine she couldn't think straight. Now, behind bars, she says it's all clear.
"Kim cried often. Actually she was very emotional. ....She talked about how she could have stopped it. ...I think Cynthia always bothered her. ...When we talked, she said that old lady did nothing to deserve this."
Casey believed Kim looked much better now than she did in 2013. "She looked good. She was fit. Her eyes were really clear. Her hair is long, graying now."
Casey says Eric looked different every time she would visit. "I would go see him. ...Sometimes he had a beard. Sometimes he didn't. I never knew which Eric would walk in. There were a couple of times he was depressed. ...He said he didn't think they should kill him."
Casey says he never admitted to being afraid of the death sentence, but there were times she showed up and he looked afraid.
Kim and Eric also sent Casey more than a dozen letters.
"In one of the many letters, he quoted Mother Teresa," said Casey reading from her novel. " 'In the final analysis, it is between you and God. It was never between you and them anyway.' "
Eric tells Casey he's converted to Catholicism behind bars.
Last month, Kim mailed a Christmas Card to Casey. The front of the card read: Jesus is the Light of the World.
Kim Williams was sentenced to 40 years in prison.
Eric Williams is appealing his death sentence.
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