"The injuries this little boy received are entirely consistent with and directly attributable to the fall that he had two days earlier," says Dr. Ronald Uscinski, a neurologist who has specialized in pediatric head injuries.
He believes Cameron began to have internal bleeding around his brain after he fell and hit his head on Friday: "It was the effect of the blood on the surface of the brain provoking a seizure. When he seized, he obstructed his airway and he aspirated and he died … Nothing need have happened on Sunday. One seizure would explain everything."
To bolster their case that Cameron was injured on Sunday, the state turns to Dr. Randall Alexander, an authority in the field of pediatric head trauma.
"Some adult-size person shook this child very violently, perhaps also hit their head against something in the process of that. And from that point on, the child basically was unconscious and dying," says Alexander.
The prosecution's experts agree, but they disagree as to what exactly happened Sunday. Dr. Krouse thinks the baby was thrown against something soft. But Dr. Alexander thinks Cameron was shaken first: "The kind we see with Shaken Baby Syndrome looks more like this. This is a brain-breaking force. Once they have this, they're not recovering."
Estrada thinks this battle of experts may actually help his client.
There is also another concern. A court takes away Cassie's other son, 2-year-old Peyton – contending that he could be at risk in the Fox household.
"We have fought so hard to keep our family together. I couldn't go through losing Peyton," says Cassie.
Peyton will live with Patrick Herring – father to both Peyton and Cameron – even though he hasn't seen much of Peyton in the year since his bitter split from Cassie.
"I was scared to death for Peyton. Cameron's death wasn't an accident. So therefore I do know that something was wrong, something went wrong in that house," says Patrick Herring.
But Cassie disagrees, and vows to fight to get her son back: "I feel we have done nothing wrong to have Peyton taken away from me."
Cassie hires custody attorney DeeAnn Smith to help her. But Billy, facing charges in the death of a baby, isn't allowed to see Peyton until his criminal trial is resolved. Cassie, who is facing no charges, is allowed only a few hours a week with her son for supervised visits.
When Peyton's third birthday rolls around, Cassie plans a party at the community center. She later finds out that her son is sick. "This happens all the time. He's always sick, he's always sick," says Cassie.
A week later, in a desperate attempt to win back custody of Peyton, Cassie and her lawyer get the judge to call an emergency hearing. They use the birthday party incident to argue that keeping Peyton with his father is dangerous to the child's health - pointing out that Peyton's been sick a lot recently. In a surprise move, the judge agrees.
But they're blindsided as they go to pick up Peyton. After the judge is briefed on the charges against Billy, he changes his mind and decides that Peyton will stay with his father.
"I felt like Peyton was ripped away from me. And I'm going to fight until the day I die for my son," says Cassie, who vows to keep her family together.
"I had Peyton taken away from me the day after Cameron's funeral. We have had one disappointment after another," says Cassie, who decides to marry Billy and make their commitment official. And now, there's a baby on the way, too - all while Billy faces a possible life sentence.
"You're guilty until proven innocent," says Billy.
In December 2002, the Fox family welcomes their newest member, Bailey. But joy quickly turns to sorrow. Armed with a court order, two social workers from Child Protective Services arrive at the hospital to take Bailey - not yet one-day-old - away from his mother. The family has an hour to say goodbye.
Geoff Wool, the CPS spokesperson for Texas, makes no apologies for the decision: "That's our responsibility to make sure in an investigation like this, where a child has died, that the other children are protected."
Cassie offered to leave Billy, move out and raise Bailey on her own, but Child Protective Services said that wouldn't help. Their experts now believe Cameron could have been injured an hour or two earlier than they first thought - and since that includes time when Cassie was still home, she's now a suspect, too.
But since other experts aren't so absolutely certain as to when the injury happened, Child Protective Services now says it isn't sure who hurt Cameron.
"Either one of them could have been the ones who actually inflicted the damage," says Wool. "We feel like there is evidence there that suggests that Cassie may have been responsible for the death of Cameron."
"That's a case of reasonable doubt right there," says Billy's lawyer Bob Estrada, who believes that CPS' position now confuses the criminal case against Billy. "I want them to continue to disagree."
Meanwhile, Billy's newborn son has been placed with his grandmother, Donna. Cassie is allowed visits to breastfeed. And Billy is allowed only supervised visits with Bailey, a few hours a week. It's an unusual arrangement at best.
But the stress is beginning to affect Billy. And with his upcoming trial, Estrada is worried.
"He doesn't know if after the trial he's going home to his family or if he's going to be in custody. That's got to be affecting him," says Estrada. "There is probably no worse case to go to trial on than an infant mortality. It's going to bring out all the emotion."
Most importantly, Billy plans on taking the stand to tell his side of the story.
Billy Fox braces himself for his upcoming trial, now only a few weeks away. The charge - injury to a child - carries a potential life sentence.
Just eight days before trial, prosecutors, apparently worried about losing this case, unexpectedly offer Billy a phenomenal deal -- no jail time at all in exchange for a plea of "no contest."
That is, Billy wouldn't admit guilt. He'd only have to concede that, given the evidence, a jury could find him guilty.
Billy says forget it. He says he's determined to clear his name: "We are not accepting a plea bargain."
"He's standing up and saying, 'I'm an innocent man and I'm not going to do anything that would make anybody think that I am anything but an innocent man,'" says Estrada. "And a no contest plea is not good enough."
On April 17, 2003, his case goes to court. But before the proceedings begin, Billy decides to accept the state's offer - 10 years probation for a plea of no contest.
"It was the scary thought of just not knowing what was gonna happen to you after you put your life in 12 people's hands," says Billy. "And I know that nothing happened to Cameron on Sunday. He was fine until he got his seizure."
The criminal case now is behind them, but there will be more days in court - like fighting for shared custody of Cassie's son, Peyton, who's been living with his father. And getting full custody of newborn Bailey, who's been in the care of Billy's mother.
But Child Protective Services, which took Bailey away at birth, has done a complete about-face and now is recommending his return. The judge agrees.
The Foxes feel they've a chance at last for a new beginning. But sadly, one without Cameron, who now would have just turned 3.
"Our family will never be the same, our marriage will never be the same," says Cassie. "Just nothing will ever be the same."
If Billy Fox completes his 10 years probation without any problem, then his "no contest" plea will be permanently removed from his record.
Then there's the ongoing custody fight over Peyton. He's now 5, and a final hearing is set for April with Cassie and Billy seeking to share custody with Cassie's ex-husband.
As to the issue at the heart of this case -- the shaken baby syndrome --
the American Academy of Pediatrics tells doctors that whenever they see injuries they believe are caused by shaking, they should presume that it's child abuse.
But critics say "shaken baby" is often misdiagnosed -- and that more research is needed so doctors can better recognize what evidence of child abuse might be, instead of just a tragic accident.