House Oversight Committee Chairman James Comer, R-Ky., warned Sunday that “something sinister could be happening” after 11 scientists mainly tied to the U.S. nuclear and space research programs reportedly died or went missing under mysterious circumstances, raising urgent national security concerns.

Comer said on “Fox & Friends Weekend” that when he first heard about the disappearances, they sounded like “some kind of crazy conspiracy theory.” But the details of the case changed his mind and prompted him to alert multiple government agencies.