“not CIA, curious.” Actually, not so curious. The CIA is intelligence gathering outside the US for mainly political policy purposes. The Defense Intelligence Agency (DIA) is part of the Department of Defense and was created by Robert McNamara for him to have a single DoD agency that would provide military intelligence to him that was separate from the 3 service (Army, Navy/USMC, Air Force) intelligence organizations during the Vietnam War. Army counter-intelligence is the logical investigator for this case. The FBI handles foreign spying on US soil, the IRS would have been involved for the spy not reporting whatever amount the ChiComs paid Hansen not being reported on his taxes; and the Dept Commerce for industrial secrets. Thus the CIA wouldn’t have been involved.
He also sold export-controlled Technology to persons in China.