The incidences are especially dubious given the scientists' work on cutting-edge, sensitive UFO and nuclear technologies. Some analysts believe the occurrences are related to the growing coverage of "aliens" and UFOs in recent years.

"It does appear that there's a high possibility that something sinister is taking place here," top House Oversight Committee Republican James Comer recently told Fox News. "It's very unlikely that this is a coincidence. Congress is very concerned about this." Comer called the issue a national security threat.

FBI Director Kash Patel told Newsweek that his agency is "working with the Department of Energy, Department of War, and with our state and local law enforcement partners to find answers." Patel said the FBI started its probe last week, adding that they're going to look into "whether there are connections to classified access, access to classified information and or foreign actors."

President Donald Trump called the incidences "pretty serious stuff." He told reporters last week that "some of them were very important people, and we're going to look at it over the next short period."

The deaths and disappearances number 11, although some of the connections are less apparent than others. Comer said the House Oversight Committee sent notices to the FBI, NASA, the Department of Energy, and the Department of Defense. "Those four agencies were predominantly the agencies that those 11 individuals were affiliated with," according to Comer.

William McCasland

Among the more high-profile disappearances is that of a retired Air Force major general named William Neil McCasland, who vanished from his Albuquerque, New Mexico, home on February 27. McCasland "oversaw classified space weapons programs and led research at Wright-Patterson Air Force Base in Dayton, Ohio, during his time in the military," according to reports. "The base has long been rumored to contain extraterrestrial debris from a UFO crash in Roswell, New Mexico."

McCasland disappeared without his phone and glasses, while his firearm went with him. Local authorities launched a massive search mission that included "drone operations, helicopter support, ground searches with Search and Rescue teams, and K-9 searchers," according to local reporting. The local sheriff's office said investigators also "contacted more than 700 homes" and asked for "security video and information."

The first missing-persons alert hinted that McCasland may have suffered a neurological problem, possibly Alzheimer's, and walked off in a state of confusion. But his wife dismissed the theory. "He was not confused and disoriented," Susan McCasland said in a social-media post.