The mysterious list of dead and missing aerospace scientists and experts continues to grow as it has been learned that an Air Force veteran who agreed to testify before Congress about UFO programs died of a what was ruled an “accidental drug overdose” just months before the hearings.

The New York Post on Saturday reported it learned of the death of Matthew James Sullivan, 39, who died in his Falls Church, Virginia, home on May 12, 2024, from “a lethal mix of alcohol, alprazolam, cyclobenzaprine and imipramine,” according to the Northern District Office of the Chief Medical Examiner.

Alprazolam is an anti-anxiety medication, while cyclobenzaprine is a muscle relaxant and imipramine is a drug for children used to treat anxiety and bedwetting. All are prescription drugs.

According to a letter obtained by the New York and California tabloid, Sullivan’s death is of “grave concern” to Rep. Eric Burlison (R-MO), with the congressman referring the death to the FBI due to what he called “implications for national security.”

“Mr. Sullivan’s death was a local Virginia medical examiner case, and the manner and circumstances of his of death raise substantial questions, as he was preparing to provide testimony to Congress,” the April 16 letter addressed to FBI Director Kash Patel read. “The sudden and suspicious circumstances surrounding his death raise significant concerns about potential foul play and the safety of other individuals involved in this matter.”

The FBI indicated in a statement that Sullivan’s death could be under investigation along other missing or dead US scientists and experts, the number of which ranges from 10 to 12, depending on what official titles are counted.

Many had access to highly classified government secrets.

Burlison argues that Sullivan could very well be number 13 on the list, explaining his concerns in an interview with Fox News.

“While we do not comment on specific incidents, the FBI is spearheading the effort to look for connections into the missing and deceased scientists. We are working with the Department of Energy, Department of War, and with our state and local law enforcement partners to find answers,” the FBI said, according to the Post.

As detailed in his obituary, Sullivan earned a Bronze Star for valor in Operation Enduring Freedom and later had several top-secret posts, including with the Air Force Intelligence Agency, National Air and Space Intelligence Center, and the National Security Agency.

The Post’s report continued:

Sullivan held “the burden that a select few in this nation have of truly understanding what’s going on,” retired Major Gen. David Abba, who served as director of special programs and later as director of the Department of Defense Special Access Program Central Office said at the funeral.

Sullivan was part of a so-called legacy UFO program — the US government’s crash retrieval program — that has operated for decades in the shadows across several executive branch agencies, sources told The Post.

Unnamed sources also told the Post that Sullivan had “personally seen UFOs” the federal government had retrieved and would have revealed the legacy program at the congressional hearing scheduled in November 2024.

Other UFO whistleblowers have said they faced threats to their safety after coming forward with information.

David Grusch, the Air Force and intel community veteran who generated national headlines when he testified to congress in 2023, wrote a letter the year before to the Intelligence Community Office of the Inspector General (IC OIG) that he faced reprisals after reporting evidence of UFOs, now designated by the federal government as UAPs or Unidentified Arial Phenomena.

Grusch testified that the U.S. was in possession of UAPs and non-human “biologics.”

“A version of Grusch’s letter was sent to the IC OIG and included information regarding Sullivan’s death,” the Post reported sources saying.

The agency told the tabloid, “IC OIG can neither confirm or deny the existence of any ongoing or potential investigations.”

Contributor Lowell Cauffiel is the author of the New York Times true crime best seller House of Secrets and nine other crime novels and nonfiction titles. See lowellcauffiel.com for more.