The only uniformed services branch under DHS is the Coast Guard, so if the OP is correct in talking about DHS and not DoD, it must have had to do with that branch.

you could type "air force general conviction" into any number of search engines... apparently there's only been one.

I searched "DHS court-martial general" and the only thing that came up was the Air Force court-martial I linked to, and I don't see the DHS connection you mentioned. The Coast Guard is under the DHS, the Air Force is under the Department of Defense.