The daughter of the dead nuclear lab worker found in a New Mexico forest claims the truth about her mother’s disappearance has been twisted by those allegedly trying to find her.
Sierra Casias, 19, took to social media just weeks before police identified the skeletal remains found in Carson National Forest as her mother, Melissa Casias, an administrative assistant at the Los Alamos National Laboratory, who had been missing for 11 months.
The teen said there had been multiple ‘false claims’ made about her mother, including allegations that she owned and carried a handgun and scandalous rumors about her personal life, which Sierra claimed were spread by a private detective.
The teen posted on Facebook in early May: ‘The information being shared is largely either publicly available material presented in a misleading way or statements that are simply untrue.’
‘The statement that Melissa owned or routinely carried a handgun, specifically described as a “Glock subcompact 9mm” is inaccurate. She could not legally purchase a firearm and did not have one.’
Casias, who vanished without a trace on June 26, 2025, was discovered in the McGaffey Ridge area of Carson National Forest next to a handgun on May 28 by a local hiker.
While the circumstances surrounding Casias’ disappearance are still a mystery and have been linked to a string of missing nuclear workers in the US Southwest, Casias’ daughter slammed other claims allegedly made by an investigator hired to find the 53-year-old.
‘This individual has been “hired” by members of my mother’s family. He has made repeated accusations toward me and my family while failing to provide any meaningful contribution to the actual search for my mother,’ Sierra said.
Melissa Casias (Left) pictured with her daughter, Sierra. Her daughter is believed to be the last family member is see Casias alive on June 26, 2025
The final image of Melissa Casias alive came from a surveillance camera near State Road 518 in New Mexico, approximately three miles from her home
‘Instead, the focus has consistently been on targeting my father rather than advancing the investigation,’ the grieving daughter added.
Sierra did not reveal the name of the private investigator she was making the claims about.
However, the Daily Mail has learned that Arizona-based investigator Thomas McNally has been working on the case on behalf of Sierra’s grandparents, Joe and Joanne Mondragon.
In April, McNally claimed: ‘What the attention should be on is that there’s a 53-year-old woman who’s missing and has a family who love her, while the husband is out trying to date other women and doesn’t care about her.’
He has also claimed that Casias’ ‘skeletonized’ remains were found propped up against a tree in the New Mexico forest and there was a gunshot wound to the skull.
New Mexico State Police announced that they identified the remains as the missing nuclear lab employee, but told the Daily Mail the medical examiner was still working to officially determine Melissa’s time and cause of death.
Sierra blasted the narrative that her father, Mark Casias, was having any marital troubles and fought over money issues with Melissa before the LANL employee vanished from the family’s Taos, New Mexico residence.
‘Claims that my father was blaming my mother for our financial situation or speaking negatively about her from the beginning are not accurate,’ the teen posted.
Melissa Casias (Left) pictured with her husband Mark Casias
New Mexico State Police have stated that the body of Melissa Casias was found alongside a handgun in the McGaffey Ridge area of the Carson National Forest (Pictured)
‘I was consistently with him and present for the conversations being referenced. He did not have a full understanding of the financial situation early on,’ she added.
‘Much of the information was still being uncovered, documented, and pieced together over time and still is to this day. It is misleading to suggest he was assigning blame for circumstances that were not yet fully known.’
Before her mother’s remains were discovered, Sierra revealed that she was already pursuing legal action related to the inflammatory claims made against her parents.
She also alleged that comments that questioned the private investigator’s remarks or supported her father were mysteriously deleted or blocked online.
‘Spreading misinformation in a situation this serious is damaging to me, to others who care about my mom, and to the integrity of the case itself,’ the teen declared.
Sierra also clarified questions and criticisms regarding the family’s actions following her mother’s disappearance last year, including changing the locks of their New Mexico home and throwing out her mother’s belongings.
The teen claimed that their home had been previously broken into by her ex-boyfriend and that disputes with other family members had led the family to secure the home as Casias’ disappearance gained national attention.
Sierra also said her mother ‘struggled with hoarding and accumulated a significant volume of unnecessary items,’ leading her and her father to take the excess to a local dump as the search continued.
Melissa Casias worked at the Los Alamos National Laboratory, a long-running nuclear research facility, before disappearing on June 26, 2025
Casias was last seen walking alone in New Mexico after dropping off her husband at work at Los Alamos National Laboratory, but not reporting for work herself
The teen did not address ongoing concerns that her mother’s case may be tied to the larger investigation into the growing number of scientists, nuclear lab workers and former military officials who have died or disappeared in recent years.
The wife and mother was also one of four known people tied to US nuclear facilities to vanish without a trace in New Mexico over the last year.
Fellow LANL employee Anthony Chavez, 79, worked at the lab until his retirement in 2017, although his role there has not been made clear. He vanished without a trace after walking out of his home on May 4, 2025, just seven weeks before Casias.
Meanwhile, government contractor Steven Garcia, 48, vanished without a trace on August 28, 2025. He was last seen leaving his Albuquerque, New Mexico, home on foot, carrying only a handgun and no identification.
An anonymous source told the Daily Mail that Garcia worked for the Kansas City National Security Campus (KCNSC), a major facility in Albuquerque that plays a key behind-the-scenes role in building nuclear weapons.
The mysterious disappearances came to light after retired Air Force General William Neil McCasland vanished from his New Mexico home in February.
The general had previously been in charge of the Air Force Research Lab, which worked together on national security projects, especially research involving America’s nuclear capabilities, with these labs.
