You never heard the theory because there was too much public noise about convicting Scott Petterson, despite the fact that there was so much exculpatory evidence. For example:
1. Men who have affairs rarely kill their wives, they leave them.
2. Men who will kill their wives for another usually woman don't kill their kid(s).
3. Men with no record of violent behavior/spousal abuse very, very rarely go from peaceful to double murderer in one jump.
4. Guys who are as dumb as Peterson is leave some kind of evidence of a crime, yet there was no evidence. The guy who can be so detail oriented as to not leave a trace of physical evidence is not likely to be dumb enough to tell the cops he went fishing exactly where the bodies were found.
5. Men who kill their spouses tend to inflict a great deal of damage to the body as a means of emotional release, yet there were no indications of this.
6. Anyone who is threatened with the possibility of the death sentence will at least talk about making a deal with the prosecution. Scott Peterson never asked for, or negotiated with the prosecution, for a deal.
7. Bodies (or anything) that's dumped into a body of water with fast-moving currents do not wash ashore exactly where they were suspected of being dumped.
8. Bodies that wash up do not end up twenty feet from the high-water mark and in rocks.
9. Bodies only float, and thereby wash ashore, when gases build up within the abdomen, and if the baby was seperate from the mother, it's obvious her abdomen was not intact enough to retain those gases.
10. The small body of a fetus would not drift at nearly the same rate as that of the mother (assuming they were both floating/drifting, which is nearly impossible) and would likely be found miles from the mother, not less than one mile.
Now granted, none of the things above are 100% hard-core certainties, and there are exceptions to every rule. But for Scott Peterson to be guilty, he would need to be a very tiny exception to every one of the above situations, and that just doesn't happen. Even if you're willing to accept that he might have beat the odds in a couple of places, that still creates a HUGE degree of reasonable doubt.
Now, let's look at Amber Fry:
1. The "Other" woman or man is far more likely to kill the spouse of their loved one.
2. Women will see another woman's child as a barrier to her getting/keeping her man and will kill an unborn/newborn child.
3. Women have been known to go from zero to murderer for emotional reasons.
4. Amber Fry comes off a lot smarter than Peterson, and would likely not kill Laci in her own home, hence the absence of evidence in the Peterson home, car, boat, etc.
5. The fact that there were minimal wounds on the body shows that the killer likely did not know the victim personally.
6. There's two reasons why someone in Peterson's position wouldn't try to make a deal: Either he's innocent, or he's innocent but protecting someone... like Fry. Don't forget that he never told Amber he did the killing, only that he thought he knew who did. And he told that to Amber and no one else... makes you think.
7. Bodies (or anything) that's dumped into a body of water with fast-moving currents do not wash ashore exactly where they were suspected of being dumped, which means that the only way they could have gotten there would be if they were placed there. The odds of the bodies showing up exactly where Scott said he went fishing are astronomicaly high, but the odds of someone who wanted to put the blame on Scott putting them there are pretty low.
8. See item 7 above.
9. See item 7 above.
10. The body of a fetus drifting ashore less than a mile from the body of the mother, in water conditions like those, is unlikely. But a distance of less than a mile is what you could expect someone who was seeding the bodies would be willing/able to walk with a dead fetus's in order to make it look like they hadn't drifted up together (which would be incredibly suspicious.)
If you look at the trends, it is far more likely that Laci Peterson was killed by a woman, for emotional reasons, and was assisted by an UNSUB after the crime. That UNSUB might be Scott Peterson, but that's unlikely as she would have only needed help with moving the bodies, and I can't imagine Scott going along with dumping the bodies right where he said he had been fishing. That location had to have been picked in order to place suspicion on Peterson. My bet would be it was a friend of hers or a sister. Hopefully, someday one of them will crack and spill the beans.