"I'm here to try to do the right thing for someone who deserves it. And that's the only reason I'm doing this," she says. "He's one of the people who are close to me whom I care about and whom I love."
Her current husband, Clint Shelton, is doing life for a murder he says he didn't commit. The two first met in Mullin, Texas, the quiet town where Clint grew up.
In 1981, Shelton walked into Clint's family store, which used to be a thriving gun shop. She had taken a shotgun in to be repaired, one thing led to another and they got married.
"He just seemed like a, you know, kind a man-of-the-West type of person. And this is such a hackneyed phrase, he was there for me," says Shelton. "He was there for me because it was this - when this - shooting of the reporter thing in Houston was all going on."
"She was brighter than most of the folks around, well, brighter than just about everyone that was raised or that lived where I was raised," recalls Clint.
But his father, Richard, never warmed up to his daughter-in-law: "She intelligent. Don't think she's not intelligent. And she's mean to go with it. She's a bitch. 18 karat."
They moved to Dallas, and Clint found work where he could, sometimes working for the local constable. Shelton convinced a judge to allow her conviction for shooting Taylor to be set aside. No longer a felon, she went back to practicing law.
Michael Hierro came to Shelton as a client when he was charged with robbery. His wife, Marisa, went to work for Shelton, and soon became the office star.
"She was simply indispensible. She would do everything for you that you needed done, whatever it was," recalls Shelton.
Seven months after Marisa began working for Shelton, she left and opened her own immigration consulting business in downtown Dallas. Soon, she and Shelton were accusing each other of scamming their clients. And things between them became nasty.
"She was threatening me, she was screaming at me," says Marisa. "She told me that I wouldn't live to see Christmas."
Shelton denies she ever threatened Marisa, but someone was out to get the Hierros. On the night of Dec. 20, 1999, Michael and Marisa drove up to their new home in Rowlett, a Dallas suburb. Michael stepped out of the car and into an ambush.
Det. Supervisor David Nabors says after shooting Michael Hierro, the masked gunman took aim at Marisa as she ran: "He got a live round in there, closed the shotgun, and then fired at her ... striking her in the arm, and upper chest and couple of pellets in the face."
Marisa says as she lay playing dead, she heard a familiar voice coming from a second masked figure, urging the gunman to shoot again: "She said, 'Don't be a pussy. Do it,' and he told her, 'I did. I shot her.'"
When they left, she says she stumbled to a neighbor's house for help.
Marisa eventually said it was Clint who pulled the trigger, but Catherine Shelton was calling the shots. Why is she so certain? "Because she spoke," says Marisa. "She said it. I heard her voice. I heard her."
A lot of other people thought the Sheltons were involved, and many of them called police when news of the shooting got out.
But there was one call that quickly proved to be the most important - and it happened after one officer visited a nearby porta-potty.
"He shined his flashlight in the Portolet and discovered a mask and two latex gloves," says Nabors.
The mask was made of pantyhose, with a hole cut out for the eyes. There were tell-tale hairs and saliva on it, and it was sent to the lab for DNA work.
"The DNA went to astronomical numbers," says Prosecutor Toby Shook, who had all he needed to indict Clint Shelton. "The scientists said it was him, no doubt about it."
But Shelton has never been charged: "I didn't understand why they didn't arrest me, because remember that she was saying that I did it."
During Clint's trial, her name, and her feud with Marisa, came up a lot.
"Catherine Shelton's name came up because that was what the motive was," says Shook.
Clint never denied putting the mask and gloves in the porta-potty. But he says he did that the night before the murder. His explanation is a little complicated, but he says he was planning to divorce Catherine, and wanted to call Marisa as a witness in his case. He says he was lurking here outside her home trying to make sure this is where she really lived.
"I didn't want her to be able to identify me. That's why I was wearing the mask," says Clint. And he said he wore the gloves in case he got too close to the house. "I was gonna touch the house, possibly, as I walked along it. Or the cars. I didn't want to leave any fingerprints."
Clint was contradicted by the porta-potty cleaner who testified that he cleaned the facility just hours before the murder -- the day after Clint said he discarded his mask and gloves.
"It was just a ridiculous story and it was just an attempt for him to cover up his guilt," says Shook.
It took the jury about three and half hours to find Clint Shelton guilty.
But now, Shelton is pushing to get the case back in court, in her own way. And she intends to name the person she says was really behind the murder.
It's been nearly four years since Clint Shelton was sentenced to life for gunning down Michael and Marisa Hierro. But he has always insisted that he was at home at the time of the murder, and so was his wife, Catherine.
"I believe they were after Catherine. I guess they thought that I would lie to them and tell them what they wanted to hear about Catherine," says Clint, who claims he doesn't have any animosity toward his wife. "Why should I? She's not the reason I'm here."
"He is a decent man. And he's not going to lie to get himself out of prison if it means putting the person in there who doesn't belong there," says Shelton.
But Marisa says Shelton belongs behind bars. And she says that's why she sued Shelton for the wrongful death of her husband, Michael. However, her lawsuit didn't get very far. When Shelton and her lawyers began barraging Marisa with almost 200 requests for information, Marisa dropped the suit.
Her case was dead, but Shelton couldn't let it rest. She counter-sued Marisa for malicious prosecution and libel. She says that Marisa cast blame on her to divert attention away from the real killer.
"It is my considered opinion that Marisa is directly responsible for the death of Michael Hierro," says Shelton, who claims the ambush and the shooting was orchestrated by Marisa.
Marisa was shot in the arm and seriously wounded after the attack. But James Murphy, Shelton's attorney, believes that can be explained: "I think she was accidentally injured by a gunshot that was not intended for her."
Murphy says Marisa had been making big money defrauding immigrants who wanted green cards, and Michael knew too much about it: "I believe that Michael Hierro was - intended to die that night because he was going to blow the whistle on Marisa Hierro's immigration scam."
Marisa denies that she was promising people green cards to immigrants and charging them thousands of dollars. But documents obtained by 48 Hours show Marisa charged high fees, and several attorneys who represent her former clients told us that she did little or nothing for that money. In fact, when a lawyers group asked Marisa whether she was practicing law without a license, she said that she told them she'd shut the business down. That was just days before the murder.
Could she have been shot by a disgruntled client? "No," she says. "I'll say that her husband's serving life in prison plus 20 years for shooting my husband and shooting me."
These days, Marisa says she is hiding from Shelton. In fact, she wouldn't even tell 48 Hours where she lives, but she talked to us at a hotel outside Texas.
"I'm not comfortable with traveling to Texas. Because then, I put myself in -in Catherine's playground," she says.
Shelton says she will press her case against Marisa even if she doesn't show up, because she wants to prove that she and Clint had nothing to do with shooting the Hierros. Shelton and her lawyer insist Clint was railroaded with flimsy evidence, like when the porta-potty near the Hierro home was cleaned.
As for Shelton, Murphy says there is evidence - her phone records - that all but exonerates her from the attack. Phone records show that Shelton's mother called her house around the time of the murder and that she was talking to somebody for a good length of time that night.
"I don't know who it was that's - investigators were unable to determine that for sure," says prosecutor Toby Shook, who stands by his case that Marisa had nothing to do with the crime.
But Shelton says Shook recognized an opportunity in Marisa's story, to get her and get headlines.
"I'm the answer to the prosecutors dream. Me," says Shelton. "I'm a lawyer. Controversy has swirled around me for 25 years. I sell papers."
Now, Shelton says she's ready to duke it out in court by suing Marisa for falsely blaming her and her husband, Clint, for the crime.
"She needs to find a job, and we hope she'll stay at it for at least 30 or 40 years, because that's how long its going to take to pay for all this," says Shelton.
It is an unusual trial. There is no jury, only a judge. There's no defendant, since Marisa was a no-show, so Murphy, Shelton's lawyer, could have declared victory right after he got here. But the trial will go on. And Murphy claims it all just boils down to Marisa's accusations.
"The woman doesn't have any credibility," says Murphy. "And that's basically all the state has to implicate Catherine Shelton in this case."
Investigator Paula Cook testifies she's found Marisa used two different Social Security numbers. And she says, Marisa seems to have married Michael Hierro before she was divorced from another man. But Marisa is not only a liar, says Murphy, who claims she actually set up her husband's murder.
"We believe that she knew who it was that killed her husband because he knew too much about her immigration scam," says Murphy. "The second shot was fired to make it look like she was also an intended victim."
Murphy calls several witnesses, who testify without worrying about cross-examination. But he saves the best, Catherine Shelton, for last.
Under oath, Shelton has to face part of her own past, at least the part that involves Gary Taylor. "He came to my home to confront me and, gotta put it very bluntly, I shot the man," says Shelton.
She also takes a few verbal shots at the witnesses against her husband at his trial, and gives an impassioned defense of an imprisoned husband. And finally, she tries to set the record straight about some of the nasty things Marisa has said about her.
"I just try to keep going and - I try to do the best I can," says Shelton. "And the worst thing she says in here - this thing - says I'm a coward. My father wasn't a coward, my mother wasn't a coward."
The judge is impressed with everything he's heard - even though he's only heard from one side.
It's a big win for Shelton, and the judge rules Marisa libeled Shelton by accusing her of murder. He then awards Shelton $5 million in damages and says, "That based on the evidence presented Catherine Mehaffey Shelton is actually innocent of the allegations of murder and assault."
But Det. Nabors says the fact that the judge in Dallas signed an order saying Catherine Mahaffey Shelton is actually innocent "means nothing." He says despite Catherine's victory in civil court, she could still face criminal charges: "We haven't been able to eliminate her as a suspect."
And prosecutors say Catherine's case will have no effect on Clint's life sentence.
Marisa Hierro wouldn't meet with us again. but through email she vehemently sticks to her story, and vows Catherine will not get away with her husband's murder...
Meanwhile, Catherine Shelton is still practicing law, after weathering all the storms and suspicions that have battered her for the past 30 years. It's a career she says that is more than a profession, almost a calling.
"When I was little, about five or six years old, I wanted to become a priest. I just loved the idea of confession, 'Whose sins you shall forgive, they are forgiven,'" say Shelton. "I'd liked that idea of being able to help somebody to get back on track. As time went on, I realized I couldn't become a priest, but I became a lawyer. I try to fix lives that have gone awry."
Catherine Shelton was in jeopardy of losing her law license when the Texas bar leveled more than 20 counts of professional misconduct against her. The charges included false advertising and overcharging clients.
Since 48 Hours first brought you this story last fall, Shelton settled the case by agreeing to a fine and a three-month suspension of her license. She's now on probation and back in business.