Slater was taken into custody in Nebraska on Friday on a three-count federal indictment and was expected to make an initial court appearance on Tuesday.
Slater, 63, was a retired lieutenant colonel in the US Army who later joined the Air Force as a civilian employee, was charged with three counts of disclosing classified material.
The indictment states that Slater sent classified emails and online messages about the Russia-Ukraine war to an individual claiming to be a woman residing in Ukraine.
The who called Slater her “secret agent” and “secret informant love,” was not identified by name in the indictment.
According to the Justice Department, Slater was assigned to US Strategic Command at Offutt Air Force Base in Nebraska, faces a maximum sentence of 10 years in federal prison for each count if convicted.