"I'm not the one who's sick, John."
Linda suffered from limp hypoplasiam, being born with her right leg missing at the knee down. This left her having to rely on a prosthetic limb to go around. She eventually married a mortician named John Nelson, and their marriage proved to be happy. Having a severe God complex, John felt that it was his duty to give Linda a real right leg, giving him the idea of transplanting a foreign leg onto her knee. This motivated him into starting his killings; all the while, Linda was aware of John's experiments but believed that he was merely testing on mice.
By the end of God Complex, she became aware of the true nature of her husband's experiments when John takes her to the garage with the intention of amputating the right leg of his fifth victim, Donna Sullivan, and she is shocked. Donna then ambushes her and holds her at knifepoint with a scalpel, but John is able to sedate her, just as the BAU arrive and hold John at gunpoint. However, John threatens to inject Donna with potassium chloride, an injection that would force a heart attack, killing her. Reid tells Linda to convince John to put down the syringe, which she does and is successful. As John is arrested, she sobs and hysterically cries out his name.