The death of Los Alamos National Laboratory worker whose remains were discovered nearly a year after she went missing remains shrouded in mystery — after medical examiners revealed they can’t determine who left her with a fatal gunshot wound to the head.

Melissa Casias, 54, disappeared in June 2025 while working at the New Mexico laboratory, where nuclear weapons research continues and the first atomic bomb was developed.

Her daughter reported her missing after finding Casias’ two phones, wallet, identification and laptop at her Taos, N.M., home, but no sign of her mother.

In late May, almost a year after her disappearance, a hiker stumbled upon Casias’ skeletonized remains in a secluded stretch of northern New Mexico, with a handgun lying close by.

An autopsy released this month determined that a gunshot wound caused Casias’ death, but investigators could not conclude whether it was self-inflicted, the Los Angeles Times reported.

Casias’ remains were in an “advanced state of decomposition” when she was found, according to the New Mexico Office of the Medical Investigator, and dental image comparisons were required to identify her.

The condition of her body also limited investigators’ “ability to estimate the range of fire, other possible injuries involving skin, soft tissues and organs, and underlying natural disease,” the report said.

Casias’ family has pushed for a more thorough investigation and maintained that they do not believe she killed herself, according to the Times.

“The condition and circumstances in which Melissa’s remains were ultimately discovered have only raised more questions for her family,” the family wrote on a Facebook page dedicated to finding Casias.

“Melissa was a mother. A daughter. A sister. A woman who was deeply loved. Her family searched for her, fought for her, and refused to give up on her while she was missing. They will not give up on her now.”

The unresolved findings come as Casias’ case has become part of an FBI investigation examining possible connections among the deaths or disappearances of at least 10 federal scientists or staff members tied to highly sensitive national security-related research.

Former Los Alamos employee Anthony Chavez, 79, vanished without a trace after leaving his home on foot on May 4, 2025, just seven weeks before Casias.

Monica Reza, 60, an aerospace engineer who served as the director of the NASA Lab’s Materials Processing Group, disappeared while hiking in a Los Angeles forest just steps behind two friends, also in June 2025

Steven Garcia, a government contractor working for a major facility in Albuquerque, also disappeared after walking out of his home on Aug. 28, 2025, carrying only a handgun and no identification.

Retired Air Force Maj. Gen. William Neil McCasland, 68, hasn’t been seen since leaving his home in Albuquerque on Feb. 27. The FBI is now involved in the search for McCasland, who had deep knowledge on UFOs and was involved in some of the Pentagon’s most advanced aerospace research, The Post previously reported.