In 1988 in Washington state, Stella Nickell was convicted of killing her husband Bruce, and Sue Snow, a bank manager, by putting cyanide in Excedrin capsules. The crime was chillingly similar to the Chicago Tylenol murders four years earlier. Seven people died in that case, which was never solved. That case moved Congress to enact tough tampering laws. Nickell was the first to be convicted under it. Now, private detective Al Farr and his partner Paul Ciolino are on a mission to prove what they both firmly believe: Nickell is innocent. Farr says that there is no credible evidence against her. 48 Hours reports on the search. "I am not guilty," says Nickell. "And I won't quit fighting until I prove it."