Sawtooth Slayer Method

Having read the book “The Sawtooth Slayer” by Nathan Goodwin, I decided to outline the basic methods used to figure out who was the killer. I really enjoyed the book and don’t’ intend to release any spoilers. But I figure the methodology can be useful for those of us searching for our own puzzle.

In Dec 16, 2012 we posted a search method provided by CeCe Moore which you can see here:

How to catch a killer OR learn more about your ancestry!

I want to compare the methods. I’m guessing that they aren’t all that different, perhaps only terminology differences will appear. The effort might teach me more about the overall procedures. You can work with me, and for sure, email me when I make mistakes. Perhaps we can go over the steps at the next DNA Discussions Group via Zoom.

1. DNA test

In this book, the first thing to do is to have a genetic DNA completed and get it to Family Tree DNA and Gedmatch. The following clustering steps can be done most anywhere, but the book is working with police and FamilyTreeDNA and Gedmatch are the only sites that will allow police involvement.

2. Identify clusters containing unique and in-common-with matches

The clusters are built, manually in the book. You can use auto-clustering at MyHeritage or Genetic Affairs if you wish. Clusters are subsets of the matches that contain unique matches that are in common with each other. Given subset uniqueness, each cluster should have a Common Ancestor (CA) and it is our job to find that person or pair. The book ended up with 7 clusters. Given that there are eight 2x great grandparent sets, that is about right. You start with the highest centimorgan match, select in-common-with, going no further than 10 centimorgans. Call that cluster 1. Go to the next not selected match and build cluster 2.

3. Build a speculative family tree of each person within each cluster, looking for the Common Ancestor

This is where the heavy work is involved. Build the trees at I’m seeing one tree per cluster with floating trees inside per person, because after the CA is located, all the “floats” would disappear. You are building the tree backward in time, going towards ancestors. In the book, they built the trees out to 3x great grandparents. I’m not sure why, that might be difficult in some cases.

4. Triangulate within each cluster, this then “closes” each cluster

I know what triangulate means, common segments for 3 or more people. I guess this step is just to prove that the tree building was legitimate, DNA wise. It will sure provide good documentation. Curiously, the first book in the series didn’t need this to close a cluster.

5. Reverse genealogy (p.230)

Reverse genealogy is where all known descendants of the confirmed common ancestors to the genetic network are traced, searching for the overlap between clusters. This is heavier tree building, building forward in time, sometimes using your “find living people” skills. Following the overlap between clusters should lead directly to the original DNA tester.

6. Success. Contact and adapt!

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