The autopsy report for missing Los Alamos National Laboratory scientist Melissa Casillas has been released, revealing a gunshot wound to the head but leaving the manner of death officially undetermined, deepening the mystery surrounding her disappearance nearly a year ago.
The 54-year-old administrative assistant vanished in June 2025 after dropping her husband off at the lab. Her remains were discovered by a hiker in a remote area of Carson National Forest in late May 2026, sparking a new wave of scrutiny into the case.
According to the report from the Office of the Medical Investigator, a bullet entered the base of her skull from the right side, passing through her cranium and exiting through the temporal bone. A firearm was found near her body, but the medical examiner could not determine if the death was a homicide, suicide, or accident.
The report states that due to advanced decomposition and limited information about the circumstances, the manner of death is certified as undetermined.
This ruling has infuriated Casillas’s family, who maintain she would never have left her daughter willingly and believe she was murdered.
“We want to make something very clear,” the family said in a statement. “The Mondragon family and Melissa’s closest friends do not believe Melissa took her own life.
Those who knew and loved Melissa know how deeply she loved her daughter.”
The family hired a private search team that returned to the remote site after law enforcement had cleared the area. That team discovered additional evidence, including shredded papers with handwriting recognized by Casillas’s sister, hair, clothing with possible blood stains, and even missing bone fragments.
Former FBI special agent Daniel Bruner, a crisis management expert, called the missed evidence “incredibly disturbing.” He noted that the initial crime scene response appeared to have been incomplete, raising questions about the integrity of the investigation.
“This wasn’t a little piece of fiber,” Bruner said.
“This was significant evidence that was missed. Bones, biological evidence, blood-stained clothing. Everything is part of the picture that investigators need to paint of that scene.”
The autopsy report confirms that the remains were skeletonized and showed signs of predation. The left hand and left foot were missing, with the left foot found about 20 feet away. The left radius and ulna, as well as cervical vertebrae, were later recovered by the private team.
Bruner emphasized that the trajectory of the bullet is particularly telling. The entry wound at the lower rear of the skull and the exit at the top of the head is not typical for a self-inflicted gunshot wound, he said, leaning him toward the possibility of homicide.
“If someone is suicidal, they usually put the gun under their chin or in their mouth,” Bruner explained.
“This angle is awkward. It leads me as an investigator to believe this appears to be a homicide.”
The firearm found near the body was reportedly registered to Casillas’s husband, Mark Casillas, who also worked at Los Alamos.
Authorities have not confirmed this, but the detail has fueled speculation among those following the case.
Adding to the intrigue, two of Casillas’s cell phones were factory reset on the day she disappeared. Her family says this is highly unusual and suggests someone may have tampered with the devices to destroy evidence.
“We all live and die by our phones these days,” Bruner said. “Why would her phone be erased? Why would she do that?
There’s more to this than just a hike gone wrong.”
The last confirmed sighting of Casillas came from a security camera at a local business on State Road 518. She was seen walking eastbound, wearing the same clothing she had on when she left home.
She had a backpack, but no one knows where she was headed.
New Mexico State Police have not commented on the newly discovered evidence or the autopsy findings. The family’s attorney has called for a full independent investigation, arguing that law enforcement’s initial search was inadequate.
“The fact that the family found additional remains and evidence weeks after the official recovery team left is deeply troubling,” the attorney said. “We need to know what else was missed and why.”
Bruner stressed that the undetermined manner of death forces law enforcement to treat the case as a potential homicide.
He urged authorities to re-examine all evidence, including the cell phone data, the trajectory of the bullet, and the possibility that someone transported the body to the remote location.
“You can’t say it’s impossible that someone brought her there,” Bruner said. “But carrying a body that far is a long way.
It’s more likely she died there, but we need to know how and why.”
The case has drawn national attention due to Casillas’s employment at Los Alamos National Laboratory, a highly sensitive nuclear research facility. Some have raised concerns about potential security implications, though no official link has been established.
Melissa Casillas was described by colleagues as a dedicated administrative assistant who had worked at the lab for years. She was a wife and mother, and her family says she had no history of mental health issues or suicidal ideation.
“She loved her daughter more than anything,” a family friend said.
“There is no way she would have left her behind voluntarily.”
The autopsy report also noted a preliminary toxicology screening that suggested the possible presence of marijuana in brain tissue, but the result was not confirmed with more specific testing due to decomposition. Investigators have not indicated whether drugs played any role.
As the one-year anniversary of her disappearance approaches, the lack of clear answers has left the community and the family in anguish. The undetermined ruling means the case remains open, but without a definitive direction.
“This is not closure,” the family said.
“This is just another chapter of pain and unanswered questions. We will not stop fighting for the truth.”
Bruner echoed that sentiment, warning that without a thorough reinvestigation, the case may never be solved.
He called on New Mexico State Police to release all evidence and to cooperate fully with the family’s private investigators.
“Trust has been broken,” Bruner said. “If you failed at something as basic as picking up bones and blood-stained clothing, how can anyone trust that the rest of the investigation was done correctly?”
The medical examiner’s office has declined to comment further, citing the ongoing investigation. But the report itself acknowledges the limitations imposed by the condition of the remains and the passage of time.
“Given the state of the body’s advanced decomposition and paucity of information available at the time of the writing of this report regarding the circumstances of her death, the manner of death is certified as undetermined,” the report states.
For the family, those words are a painful reminder that justice may be elusive. They have vowed to continue their own search for answers, hiring additional experts and pressing law enforcement for transparency.
“We will not rest until we know what happened to Melissa,” they said.
“She deserves that. Her daughter deserves that.”
The case has also sparked broader questions about how missing persons cases are handled, especially when they involve employees of sensitive government facilities.
Some advocates are calling for independent oversight of the investigation.
As the sun sets on another day without resolution, the mystery of Melissa Casillas’s final hours remains as haunting as ever. The autopsy report has provided some facts, but the chilling twist is that the most crucial question—how did she die?
—remains unanswered.
“We have a gunshot wound, a bullet through her skull, a firearm nearby,” Bruner said. “But the medical examiner won’t say if this was murder, accident, or something else.
That’s the kicker.”
The investigation continues, and the family waits, hoping that the next chapter will bring the truth they so desperately seek.
