getting a whole lot better. kathleen's sister candace thought peterson had killed both women. >> i have a better chance of being struck by lightning thannen finding two people that i intimately know at the bottom of a staircase. >> but to margaret and martha, the whole thing teamed absurd. the fact that michael would be accused of killing kathleen, the woman they called mom was bizarre enough. but now, their birth mom, too? what would their father have gained by killing elizabeth ratliff? >> he would have gotten two screaming little raga muffin kids out of it. that's it. there's no reason for it. >> for the investigators in north carolina, though, the death in germany became a strong building block in their circumstantial case for murder. and what's more, detectives learned that michael peterson had a secret life. secrets, tawdry ones, were about to spill out in the durham courthouse. >> coming up, enter brad, the