On a gloomy morning in Los Angeles, Monica Reza and a friend from yoga class set out on a hike in the San Gabriel Mountains.
Midway through the hike on June 22, 2025, Monica fell about 30 metres behind her companion.
Her friend glanced back to see Monica smiling and waving to say she was OK.
Monica Reza went missing while hiking in the California region. (Supplied)
But when her hiking partner looked back again moments later, Monica was gone.
Search and rescue teams searched for days for her body, but all they found was Monica’s beanie.
The director of materials processing at NASA’s Jet Propulsion Laboratory joined a growing list of US scientists who had recently gone missing or died.
That list is made up of at least 12 US scientists who supposedly all had access to sensitive government research.
Some worked for NASA, others studied nuclear science and astrophysics, and some worked on UFO research.
The nature of their work has led to speculation and conspiracy theories that they might all be connected.
It sounds like the plot of a blockbuster spy movie and is “pretty serious stuff,” according to US President Donald Trump.
“Coincidence, whatever you want to call it … but some of them were very important people, and we’re going to look at it over the next short period,” Mr Trump said in April.
FBI director Kash Patel confirms an investigation is ongoing, while Donald Trump says the matter is “serious”. (Reuters: Jonathan Ernst)
The US Committee on Oversight and Government Reform said in a letter to the FBI that the incidents were a “grave threat” to the country.
“These deaths and disappearances may represent a grave threat to US national security and to US personnel with access to scientific secrets,” the letter said.
Both the US Congress and the FBI have launched investigations into the deaths and disappearances.
FBI director Kash Patel said “we’re going to look for connections” and noted the FBI would take a closer look at “foreign actors”.
“If there’s any connection that leads to nefarious conduct or conspiracy, the FBI will make the appropriate arrest,” he said.
South Carolina congresswoman Nancy Mace posed the question many on the internet were asking.
“Who killed the scientists?”Who is involved?
According to public reports and a statement from the House Oversight Committee, the first death to cause concern was that of Michael David Hicks in July 2023.
And the most recent incident the committee believe could be linked is the disappearance of retired US Air Force major general William McCasland on February 27 this year.
Concerns of a “sinister connection between a string of mysterious deaths and disappearances” were raised by the Oversight Committee on April 20.
Not all of the people who have been linked were scientists. Some worked as security officers or admin workers at top-secret government facilities.
Here is the list in order of their death or disappearance:
Died on July 30, 2023. No official cause of death has been given.
Worked as a scientist at the NASA Jet Propulsion Laboratory (JPL) from 1998 to 2022.
His speciality study area was the physical properties of comets and asteroids.
Hicks worked on the DART planetary defence project, the Near Earth Asteroid Tracking (NEAT) Project, the Dawn Mission, and the NASA Deep Space 1 Mission.
Died on May 12, 2024, from an accidental drug overdose.
He was a former air force intelligence officer and a Bronze Star recipient for his service in Afghanistan.
Sullivan was part of the US government’s UFO crash retrieval program, sources told the New York Post.
According to those sources, he had seen UFOs and was due to testify about his eye-witness accounts at a congressional hearing in November 2024.
Died on July 7, 2024. No official cause of death has been given.
Maiwald worked as an imaging spectroscopy engineer at NASA’s Jet Propulsion Laboratory.
He was the principal investigator on Earth-observing and space instrumentation projects.
Disappeared on May 8, 2025.
Chavez is a former Los Alamos National Laboratory employee. He worked as a construction foreman at the site.
Los Alamos was the site of the US government’s top-secret Manhattan Project during World War II.
A detective investigating his disappearance said there were no indications of foul play, but also no signs that he was planning to leave.
Carl Buckland, a close friend of Chavez, said “his disappearance is extremely unusual” in a Facebook post.
Disappeared on June 22, 2025.
Reza was a metallurgist and materials engineer at NASA’s Jet Propulsion Laboratory.
She was the director of the Materials Processing Group at the NASA lab, and she co-invented a nickel-based superalloy used in rocket engines.
The 60-year-old was last seen going for a hike in the Angeles National Forest.
Disappeared on June 26, 2025.
Casias was an admin assistant at NASA’s Los Alamos National Laboratory.
Her husband also works there.
She was last seen by her husband after she dropped him off at work in the morning, before she was due to head home.
Her daughter returned home later that day and reported her missing. Her phone, purse and wallet were left at home.
A spokesperson for New Mexico State Police said they do not suspect foul play at this time.
Died on July 22, 2025, in a car crash in Alabama.
LeBlanc was an electrical engineer at NASA Marshall Space Flight Center.
He worked on nuclear propulsion projects for use in spaceflight missions to Mars.
His Tesla vehicle caught fire after leaving the road, and authorities took three days to identify his remains.
Police tracked his movements before the crash using Tesla’s Sentry Mode system, and the data showed he was parked at Huntsville International Airport for around four hours before the crash.
Disappeared on August 8, 2025.
He worked as a government contractor at the Kansas City National Security Campus.
That campus makes several “national security products” for the US Department of Energy.
Garcia’s work involved the production of non-nuclear components for nuclear weapons.
According to local media reports, he was last seen leaving his home on foot, carrying a handgun.
Died on December 12, 2025, by drowning.
He was the assistant director of chemical biology for the pharmaceutical company Novartis.
His body was pulled from Lake Quannapowitt in Massachusetts after he had been missing for three months.
The Middlesex County, Massachusetts, medical examiner stated no foul play was involved.
His wife said he had been struggling to cope with the recent deaths of his parents.
Died on December 16, 2025. He was fatally shot on his own property.
Loureiro was a plasma physicist and professor at the MIT Plasma Science and Fusion Center.
He was shot and killed in his apartment in Brookline, Massachusetts.
Police identified his shooter as Claudio Manuel Neves Valente, the same man who committed the 2025 Brown University mass shooting that occurred two days before Loureiro’s death.
On December 19 2025, Valente was found dead in a storage facility. Police were unable to establish a motive for Loureiro’s murder.
Died on February 16, 2026. He was fatally shot on his own property.
Grillmair was a renowned retired California Institute of Technology (Caltech) astronomer and astrophysicist.
His specialised study areas include exoplanets, galactic structure, and dark matter. He once detected water on a planet outside our solar system.
He was shot and killed at his property in the small rural town of Llano, Texas.
Grillmair’s alleged killer, 29-year-old local man Freddy Snyder, has been charged with murder and burglary.
Disappeared on February 27, 2026.
McCasland is a retired US Air Force major general and the former commander of the Air Force Research Laboratory.
He was once the commander of the Wright-Patterson base, which was part of the Roswell UFO incident.
The veteran was reported missing by his wife, who said he left his prescription glasses and phone behind, but took a revolver with him.
The letter from Congress sent to the FBI states there are reports of “a direct link between Ms Reza and General McCasland”.
It is alleged that the pair had a “close professional connection” through an air force-funded research program.
The 2022 death of Amy Eskridge is also considered by online sleuths to be a part of the wider conspiracy.
The House Oversight Committee letter sent to the FBI does not list her death as potentially linked.
She founded the Institute for Exotic Science in the US and specialised in quantum computing and gravity modification.
Eskridge died in June 2022, aged 34, after suffering from chronic pain for some time, according to her family. Her official cause of death has not been disclosed.
Are they really linked?
This group of people is lumped together as scientists, but in truth, the list includes an air force general, an engineer, an administrative assistant and a security official.
Those on the list who were scientists worked in different fields, and not all worked together.
Science writer, investigator and pseudoscience debunker Mick West wrote in a Substack article on April 16 that there was no unusual pattern.
“The US top secret-cleared aerospace and nuclear workforce is ~700,000 people,” he wrote.
“Ordinary mortality over 22 months predicts ~4,000 deaths, ~70 homicides, and ~180 suicides. The list has 10.
“The deaths are real. The families’ grief is real. The pattern is not.”
Families of the missing or deceased scientists agree that there is no pattern.
Two of the scientists worked at Los Alamos National Laboratory. (Getty: Joe Raedle)
“I think it’s absolute nonsense,” Louise Grillmair, Carl Grillmair’s widow, told the BBC.
“I mean, there’s the facts, and they’re out there.”
Neil McCasland’s wife, Susan McCasland Wilkerson, said: “It seems quite unlikely that he was taken to extract very dated secrets from him.”
She posted on Facebook in March that a search for her husband was ongoing, and his now-dated military clearance was “not a reason for someone to abduct Neil”.
Officials from the Trump administration have said the probe into these incidents was ongoing, but there has been no evidence presented publicly showing the cases were linked.
‘Hallmarks of a foreign operation’
House Oversight Committee chairman James Comer suggested that what has happened to this group of US scientists could be foreign interference.
“We know there are many countries around the world that would love to have our knowledge and nuclear capabilities,” he told Fox News last month.
“These are the people that were at the forefront of it, and they’re either dead or missing.”
Republican Congressman for Missouri Eric Burlison said the US public should be concerned, citing China, Russia and Iran as potential lines of inquiry.
“This has all the hallmarks of a foreign operation,” he said.
When asked about the missing scientists, White House press secretary Karoline Leavitt said: “No stone will be [left] unturned in this effort.”
“The White House is actively working with all relevant agencies and the FBI to holistically review all of the cases together and identify any potential commonalities that may exist,” she said.
White House press secretary Karoline Leavitt says the investigation will be comprehensive. (Reuters: Kevin Lamarque)
The FBI said in a statement it was “spearheading the effort to look for connections into the missing and deceased scientists”.
NASA also confirmed it was “coordinating and cooperating with the relevant agencies in relation to the missing scientists”.
“At this time, nothing related to NASA indicates a national security threat,” NASA spokesperson Bethany Stevens said.
Critics say it is merely a conspiracy theory. But some US politicians say this is sinister.
Mr Trump said no evidence of a connection has come up during the investigation to this point.
But he did remind reporters in the Oval Office that his administration was “going to be doing a full report and it’s very serious”.
In a post updating people of her husband’s disappearance, Neil McCasland’s wife said he “had access to some highly classified programs,” but that was before he retired 13 years ago.
“Maybe the best hypothesis is that aliens beamed him up to the mothership,” she concluded.