New charges have been filed in court that takes this case from the tragic to the bizarre. Now, Mary wants a divorce, claiming that Dennis is violent and sexually abusive. And Dennis has counter-attacked with allegations that Mary has a history of drug abuse and alcoholism.
The battle plans are piling up in what has become the War of the Hills. "And the War of the Hills is almost as dramatic as the War of the Roses," says Dennis, who believes Mary should not have been charged. "If they would've followed us around and filmed this thing, it would've made a heck of a movie."
In spite of Dennis' public support, Mary has thrown him out and even got a restraining order against him. "Dennis was into physical pain for sexual gratification. Both giving and receiving," says Mary. "It got to be far too much."
"That's absolutely not true. In 25 years, I never hit that woman," says Dennis, who denies sexually abusing his wife. "Absolutely not."
But Mary says she's afraid of Dennis: "He admitted openly in court, after I filed the injunction to keep him away from me, he was going to slash my face to pieces and see me disappear."
"I got so mad," explains Dennis. "I said 'You know, Mary, I'd like to get a two by four and just come and smash your face in.' Of course, I regret saying that."
But there's another casualty in the War of the Hills: their 13-year-old daughter, Kaitlin, who claims that her mother once told her that she wished Kaitlin had died in the accident instead of Amy.
"That is true. I'm not perfect, and yes, I did. And I apologized," says Mary. "And I apologize to this day. But I was so consumed with the loss of Amy."
With Mary facing homicide charges and Dennis accused of domestic violence, both parents lost custody of Kaitlin, who was sent to live with her older half-sister, Jennifer.
"I've lost two daughters. I can't accept that, I'll never accept it," says Dennis. "I'll fight until they put me in the ground."
As Mary's trial date finally nears, she has hired Tim Berry to represent her.
The trial Mary Hill has waited three and a half years for was about to begin. In August 2000, Hill's BMW slammed into a tree, killing her daughter, Amy, and Amy's best friend, Carrie Brown. "I wish I could change everything that happened that day," says Mary.
If Mary is found guilty, she faces the possibility of up to 30 years in prison. "I'll die in prison," says Mary. "This is a fight for my life."
Attorney Tim Berry, who will lead Mary's defense team, claims a malfunctioning cruise control made Mary's BMW speed out of control. He's not sure, however, if he'll put Mary on the stand.
An all-female jury was to determine Mary's fate. They must decide if she's guilty of vehicular homicide, manslaughter and negligence for Zak Rockwell's injuries.
In his opening statement, Prosecutor Bart Schneider says it's clear Mary's reckless driving killed Amy and Carrie. But Berry tells the jury the real culprit in this tragedy is the car itself. And despite Mary's well-publicized record of mental and marital problems, Berry claims his client is not suicidal or homicidal.
The prosecution, however, uses eyewitness Jimmy Arthur to prove their theory that Mary was driving out of control.
With emotions running high, Dennis Hill is called to the stand, and the lead prosecutor, Pat Whitaker, tries to use Dennis to undermine Mary's claim that the BMW was defective. When asked about the BMW, Dennis testifies that he had no problems with the BMW that day.
The jury hears nothing from Dennis about his bitter separation from Mary, or allegations of physical abuse. And Dennis tells the jury that Mary was in a very good mood just hours before the accident.
Suffering from a stomach ailment, Mary was forced to leave the courtroom. During her recovery, the jurors take a field trip to the site of the crash, to see firsthand where Amy and Carrie died.
The defense team relies on a British electrical engineer to convince the jury that the accident wasn't Mary's fault, but rather a fault in her BMW. The engineer, Dr. Antony Anderson, testifies that the reason for the accident was "a sudden acceleration event" caused by what he claims is "a rogue electrical signal."
"A rogue signal can come in and give a false command … which can affect these very sensitive electronic circuits within the cruise control," says Anderson, who believes this false command could have switched on the BMW's cruise control, triggered the accelerator and caused the car to speed up on its own.
But the prosecution's BMW expert, Mark Yeldham, twice tested Mary's BMW and found "no faults stored in the cruise control system."
Yeldham, who works for BMW, admits the company receives dozens of sudden acceleration complaints every year. But of those 50 complaints each year, Yeldham says most involve driver error.
In a final move to bolster their runaway car argument, the defense calls two drivers who claim their BMWs had also experienced sudden acceleration.
And on the last day of the trial, after three and a half years of silence, Mary is called to take the stand. Incredibly, it was the first time Brown and prosecutors have heard from Mary about the crash.
"It picked up speed. It started going faster. I released the brake and applied it again," says Mary. "The car started to go out of the lane, it was fishtailing. Everything was very quiet, and I remember looking down at the dash, and said 'Why won't you stop?'"
After five days of testimony, it's now up to the jury to decide Mary's fate.
If found guilty, Mary could spend the next 30 years behind bars. And, after just five hours, the wait is over.
The jury has found Mary guilty on all counts, a dramatic rejection of her claim that her BMW had sped out of control on its own, killing Amy and Carrie, and causing brain damage to their friend Zak Rockwell.
"I prayed and hoped that justice would come, and it came today," says Carrie's mother, Rita Brown.
Mary will remain free on bond until sentencing, but she is ordered to hand over her driver's license. As reporters mob her, Mary is too distraught to talk.
But Heather and Julie Hill, Dennis' daughters from his first marriage, have plenty to say. They contacted 48 Hours after the trial, with explosive allegations the jury never heard.
They say they know what it's like to be in the back seat of a speeding car driven by Mary. "She got mad at my dad and she tore down the highway going like 90 miles an hour. I remember I was so scared in the back seat," says Julie.
"They're angry at me over Amy's death. I'm not their mother; I'm their stepmother," says Mary. "Truthfully, if I go to jail, let's face it, it will help their father considerably with the divorce."
And it's jail time that Brown pleads for at Mary's sentencing: "Carrie will not go off to college. I will not be able to spoil her children. I will not be able to take care of them when she's on vacation with her husband, the husband she never met."
For the first time since the accident, Mary utters the words Brown has waited so long to hear: "The words 'I'm sorry' can never convey to her how I feel. I do apologize to the parents and to the families and to the friends and to everyone that knew Carrie and Amy and Zack."
"I felt like she meant it, but it's too little too late, I guess," adds Zak.
The judge then surprises everyone by ordering Mary to jail until he decides on her sentence. Even her estranged husband, Dennis, finds the sight of her in handcuffs unbearable.
"It's probably one of the worst moments I've ever gone through in my life. It hurt a lot, it really did," says Dennis. "I just think that she will just will herself to die and she'll just die in jail, and I don't know if I can really handle that."
More than three months later, a visibly shaking Mary Hill, now being treated for depression and alcohol and drug addiction, is back in court to hear the judge's decision. She was sentenced to serve 15 years in the Department of Corrections in Florida.
Mary received the sentence with some advice from Judge O.H. Eaton: "Mary Hill, I don't know what you're gonna go with your life. You're going to have to make a lot of adjustments."
Mary once had it all: a successful business, a mansion where she raised a loving family, and a world of possibilities. But now, a prison will be the only world Mary will know until she's almost 70.
But will the tragedy ever truly be over for any of the survivors? Mary and Dennis are getting a divorce.
Kaitlin, 15, is still in custody of her older sister, and must deal with the haunting memory of her mother in shackles. And Rita Brown can only dream of what her daughter, Carrie, might have become.