Hanna Lowell (Mariette Hartley) is the villainess of "SWAK," the penultimate episode of NCIS' second season (airdate May 10, 2005). She is a former activist who later became the CEO of Lowell Pharmaceuticals.
Furthermore, after the rape case involving her daughter Sarah went cold with no arrests, Hanna went off the deep end and sought to exact revenge on the NCIS, feeling that they lied to protect a U.S. Navy midshipman she believed raped Sarah. The villainess sent a letter "sealed with a kiss" that contained a genetically modified version of Y. pestis, which is Latin for "plague," causing the NCIS HQ to be quarantined after Tony DiNozzo was infected with the microbe.
After her villainous reveal, the vengeful woman was shown sitting in her office as she demanded to Leroy Gibbs that the NCIS either admit to (what she firmly believed was) their cover-up or never receive the antidote for the plague. She also revealed that she was dying rapidly from an inoperable brain tumor, stating that her chances of seeing her own sentencing are slim. Hanna was arrested anyway, and when she learned that someone has been infected, she snarled that she hoped it was a man known as Westmoreland, who she suspected of raping her daughter. Sarah later admitted that she wasn't raped, and made it up in the hopes of avoiding family embarrassment.