Detective Investigator Sean Riggs is an attorney general investigator who worked in the office of A.D.A. Page Ferguson, who was secretly his girlfriend. She had a propensity to self-mutilate, which was caused by the stress of her job, and it was bad enough Riggs would be accused regularly of abusing her.
When drug money in their investigation went missing and a dirty cop was suspected, he was one of several teammates interrogated, Ferguson presiding over the questioning. To not threaten their relationship, Riggs took a polygraph by his choice so Ferguson didn't have to question him. When the real thief, Sunny Qadri, Ferguson's friend, was revealed to be the thief, she arranged for Ferguson's torture-murder to cover her actions, as well as the killings of the mercenaries responsible.
Riggs was devastated, and when suspected because of his temperament and relentlessness in his job, he admits to his risky behaviors on the job, but he reveals his and Ferguson's relationship and how he tried to stand by her as a loving partner, regretting how still ended up killed in the end. He was thus acquitted, and Qadri and her living accomplices were accordingly charged. (SVU: "Dirty")