A U.S. congressman made a commitment on Thursday to unravel the enigma surrounding the recent cases of 13 American scientists who have either died or vanished, as President Donald Trump provided updates on the ongoing federal investigation.

“The tally has reached 13. Thirteen scientists from the U.S., all linked to nuclear and space research, are either missing or deceased,” stated Rep. Eric Burlison, R-Mo., on X. “Every adversary rejoices at our losses. These incidents weaken our nation, and I am determined to uncover the truth.”

He continued, “I directly asked the FBI if they have initiated an investigation into Matthew Sullivan’s suspicious passing. Their response was neither a confirmation nor denial. I’ve been pursuing this for nearly a year. The American public deserves clear answers from the FBI. No exceptions.”

Rep. Eric Burlison was present at a Republican Study Committee news conference, where the fiscal year 2025 budget proposal was presented at the U.S. Capitol on March 21, 2024, in Washington, D.C. (Bill Clark/CQ-Roll Call, Inc via Getty Images)

The New York Post reported that Sullivan, aged 39, succumbed to an accidental drug overdose at his residence in Falls Church, Virginia, on May 12, 2024. This occurred shortly after he agreed to testify before Congress regarding government UFO initiatives.

The Post, referencing Sullivan’s obituary, highlighted that he was a former U.S. Air Force intelligence officer who was awarded a Bronze Star during Operation Enduring Freedom. He later worked at the National Air and Space Intelligence Center, the National Security Agency (NSA), and the Air Force Intelligence Agency.

The disappearance of retired Air Force Maj. Gen. William Neil McCasland earlier this year set off the cascade of theories about the missing and dead scientists. He was the former commander of the Air Force Research Laboratory, and had connections to the Los Alamos National Laboratory, where top-secret nuclear research is conducted.

A split image shows retired Air Force Maj. Gen. Neil McCasland in the green shirt he was last seen wearing and in his military uniform. (Bernalillo County Sheriff’s Office, Neil McCasland/Facebook, Kirtland Air Force Base)

At least 13 people, including Sullivan, the vast majority of whom were involved in nuclear science and space research, have died or gone missing since 2022, some under mysterious circumstances.

Monica Reza, 60; Melissa Casias, 53; Anthony Chavez, 79; and Steven Garcia, 48, were all reported missing between 2023 and 2026, with each of their disappearances considered suspicious.

Michael David Hicks, 59; Frank Maiwald, 61; Nuno Loureiro, 47; Jason Thomas, 45; Amy Eskridge, 34; Carl Grillmair, 47; and Joshua LeBlanc, 29, all died between 2022 and 2026. 

Jason Thomas, left, Melissa Casias, center, and Frank Maiwald are among scientists whose deaths or disappearances have drawn scrutiny as officials review whether any cases are connected. (Fox News: Sierra Casias: Legacy.com)

Hicks, Maiwald and Reza were all connected to NASA’s Jet Propulsion Laboratory.

The trend caught the eye of the White House, and the FBI is investigating.

“The FBI is spearheading the effort to look for connections into the missing and deceased scientists,” the agency told Fox News Digital in a statement. “We are working with the Department of Energy, Department of War, and with our state and local law enforcement partners to find answers.”

Trump on Thursday gave an update on the investigation to Fox News’ Peter Doocy, saying the situation is “very serious” but that so far, he hasn’t seen evidence that shows a connection in the deaths and disappearances.

President Donald Trump said he wants to investigate the deaths and disappearances of 11 scientists mainly tied to the U.S. nuclear and space research programs. (Brendan Smialowski/AFP via Getty Images)

“Well, so far, I mean, they’re individual,” Trump said. “We have a lot of scientists. When you see, you know, you put together 10 it’s a lot. But it’s, you know, a very small number, compared to what overall, we have a lot of scientists. I was asking that question. Thousands, hundreds of thousands of scientists.

“So no, some of them that we looked at are very sad cases, in some cases, some were sick. Some left this earth self-inflicted. Some had other things. So, so far, it’s not a major, you know, sometime it’s a little bit of a connection anyway. And you say, ‘oh, this is, this is a terrible thing.’ But so far we’re finding that, there’s not much of a connection. We’ll let you know. We’re going to be doing a full report. And it’s very serious.”