Cayley Mandadi was a 19-year-old sophomore at Trinity University when she arrived at a hospital in Texas on Oct. 29, 2017. She was nearly naked, bruised and not breathing. Her sometime boyfriend Mark Howerton told doctors they'd taken ecstasy at a music festival, and she passed out after consensual sex in his car. She died at the hospital.

Mandadi's mother Alison Steele and stepfather Lawrence Baitland believed something far more sinister happened and set out to prove it. "48 Hours" correspondent Peter Van Sant reports on the case in "For the Love of Cayley Mandadi" to be broadcast Saturday, Jan. 20 at 10/9c on CBS and streaming on Paramount+.

At 4 a.m. on Oct. 30, 2017, Mandadi's parents woke up to an alarming phone call. They were told Cayley had been life-flighted to Kyle, Texas and had been involved in an incident.

They raced from their home in Houston to the hospital. "I saw my daughter's body smashed," Steele recalled. Mandadi was unconscious and covered with bruises. The doctor told them there was no hope for recovery. 

On Oct. 31, Mandadi was taken off life support. Steele and Baitland gave their final goodbyes before Mandadi was taken into surgery for organ donation.

The medical examiner ruled that Mandadi died from blunt force face and head trauma and ruled her death a homicide. Howerton was charged with her murder.

Howerton maintained his innocence and in December 2019 his trial began. Prosecutors alleged that Howerton beat Mandadi in his car, causing a fatal brain bleed.

Howerton's defense attorney, John Hunter, said Howerton did not cause Mandadi's injuries. He argued that her injuries were caused by resuscitation efforts by hospital staff and medical complications from taking MDMA.

After 10 hours of deliberations, the jury could not reach a verdict and the judge declared a mistrial.

While prosecutors planned to retry Howerton, Steele and Baitland decided the jury needed more information about what happened to their daughter inside Mandadi's car. Steele, a scientist, and Baitland, a NASA engineer, got to work.

"We are not prosecutors, we are not medical doctors, but we know people who have those skills and maybe we could develop a way to crowdsource some answers into this thing. And so that's what we did," Steele told "48 Hours." "We started making phone calls, we started making inquiries."

Steele said they were overwhelmed with offers from experts, including medical doctors, forensic scientists and even a medicolegal death investigator to help them examine evidence in Mandadi's case. They got all the evidence they could.

"What we did was to take that evidence and to make sense of it in a way that was not done in the first trial," Steele said.

The couple focused their attention on one autopsy photo showing a bruise in the shape of a small dot above Mandadi's right ear, and on another photo showing a larger bruise above her left ear. Steele says they landed on a theory that Mandadi's fatal injury took place when Howerton "reached from his driver's seat, hit her in the left ear and drove her head into the window and onto the lock button of the car." Now they had to prove it.

So they went to a used car lot where Baitland took photos of Steele posing in a car similar to the Mercedes Howerton drove the night Mandadi was fatally injured. 

Baitland told "48 Hours" he "photographed [Steele's] head in different positions while … holding the autopsy images, trying to see if they match up with the door and it's a near perfect match."

Encouraged by their findings, Baitland used a software program to construct a 3D model of Mandadi's head. He layered in photos of Mandadi and the autopsy photo showing that dot above Mandadi's right ear. He used a measurement from Mandadi's eyeglasses to help determine the size of the 3D head. Baitland then consulted a biomechanical expert in injury causation who examined the evidence and Baitland's research and supported his theory.

"So this gave me the confidence to go to the next step, which was to seek out [Mark Howerton's] car," Baitland said.

Baitland tracked down the Mercedes that Howerton sold in 2018. "I … reached out to some friends on social media who were … on an automotive forum and they were able to look up the VIN number of [the] car for me," he said.

At first, the new owner was hesitant to sell Baitland the car, but after learning about Mandadi's story, he agreed. Baitland said driving the car home was "torturous" but necessary for their investigation. "We had to have the vehicle to show how she was assaulted."

Baitland and Steele then commissioned a reenactment video of what they believe happened in the car. Using evidence photos, they focused on every little detail, including what Mandadi and Howerton were wearing and what items were in the back seat. They even hired actors similar in size and weight to Mandadi and Howerton. 

The reenactment video is simple: showing three angles of what Mandadi's parents and their experts believed caused the fatal injury to her head.

Prosecutors in the case told "48 Hours" they've never seen a victim's family go to such lengths before. Howerton's defense attorney, John Hunter, believes the parents' investigation is "unscientific" and fails to prove his client's guilt.

Will the parents' investigation be a game-changer for Mark Howerton's second trial? "For the Love of Cayley Mandadi," airs Saturday, Jan. 20 at 10/9c on CBS. 

In:
• 48 Hours
• Texas