3 Person Mixture #4 (Or is it 2?) The Hardest Mixture I Know

Bed Sheet Stain 1

Bed Sheet Stain 2

Suspect Underwear

Data Table Is Victim included?

The Hardest Mixture I Know We have to deal with family sexual assault cases These by definition include biologically related people Sometimes step-parent situation Sometimes biological parent situation But they all live together so no “random man”

The Hardest Mixture I Know Evidence commonly shows all alleles of both Mom and Dad (or Mom and Step-Dad) Some advantages: – Not “unrelated” people (well, step-dad) – Not “random” people Therefore, no statistics apply – “The probability of a random, unrelated person contributing to the mixture is…” If someone knows a relevant stat, let us know

The Hardest Mixture I Know OK - so we don’t worry about a stat What do we need to worry about? – Hp vs. Hd – (But I don’t know a relevant LR to use) But we are asked to answer a question: – Is the victim contributing to that semen stain found on the parents bedding and Dad’s boxers or not?

The Hardest Mixture I Know Is she “there” because it’s mixture of her biological parents OR Is she “there” because she has been sexually assaulted but her biological father These types of cases are the most difficult mixtures I’ve ever seen (obvious reasons)

The Hardest Mixture I Know So it’s what I call a “real time” LR It has nothing to do with any LR stat that I know Instead I assume each hypothesis is true and I test them Then I decide if one hypothesis is supported better than the other

The Hardest Mixture I Know How do I do that? Start with Defense hypothesis: – The evidence is consistent with a 2 person mixture of Mom and Dad only – Use the 2 person calculator with only Mom and Dad applied Does it “graph” well? Is there a “valid” combination at each locus? – In other words, does our validated PHR and P calculator show that the data “fits”

The Hardest Mixture I Know Then the Prosecution hypothesis: – The evidence is consistent with a three person mixture of Mom, Dad, AND Victim (bio daughter) – Use the 3 person calculator with all three reference profiles applied Does it “graph” well Is there a “valid” combination at each locus? – In other words, does our validated PHR and P calculator show that the data “fits”

The Hardest Mixture I Know A note about testing the three person hypothesis Bio Mom, Bio Dad, and Bio Child is worst case scenario for “not excluded” options – The “double” or “circular” sharing types – We will not get much in terms of P and PHR The “graph” will be pretty lousy BUT we can still see if there is a “valid” contributor option in our 3 person calculator

The Hardest Mixture I Know The three person graph for this scenario at the time this handout was prepared is basically worthless At all the loci where a “not excluded” combination is viable, we see empty space in the graph – all we get is the name of the locus on the X-axis At all loci where two contributors share a type, we don’t even get an X-axis label

The Hardest Mixture I Know So I just will give a “count” for the number of loci that show a valid three person option Our programmers are working feverishly to get this working better by the workshop – (Buy stock in Mt. Dew) Show P for the one person that doesn’t share with a designation that the other 2 share a type Show a designation for “not excluded” loci Ultimately solve the “not excluded” dilemma(?)

The Hardest Mixture I Know We made a bunch of validation samples from three volunteers I know very well – I had to bribe my daughter – She felt she deserved a new Barbie in exchange for her “Buckle DNA” We made it “worst case” by keeping Mom and Dad equal contributors When either Mom or Dad is a minor, it makes it easier to determine if Daughter is “really there”

The Hardest Mixture I Know Because there are so many “not excluded” options, we have to do a further test than just “viable” at our normal validated PHR of 50% We will instead test at 80% PHR In real life, you would do this in iterative steps and watch what happens for each hypothesis maybe all the way from 50-90% For this hand out, it’ll just be 80% and 90%

The Hardest Mixture I Know First we test to see if all three people have relevant alleles present to check if Mom or Dad is low level or dropping out but daughter still all there All concerns about <300 etc. are thrown out This is testing what fits, not worrying about a potential missing allele from a random, unrelated person – these are all related people living together

Sheet Stain 1 Mom and Dad at 80% PHR Support at 11 loci (not counting Amel) But Amel can be useful Suspect varies 43-69% 43-59% if you ignore D16 (16% window)

Sheet Stain 1 Mom and Dad and Daughter at 80% PHR Support at 9 loci Lots of “not excludeds” and “2 people sharing types” loci – won’t graph

Sheet Stain 1 Answer Remember this is a mixture I made in the lab Hp – 11 of 15 loci show support (not bad) Hd – 9 of 15 loci show support (still OK) I’m going “inconclusive” as to V’s status Not much difference The mixture is really only Mom and Dad

Sheet Stain 2 Mom and Dad at 80% PHR Support at 9 loci Proportions not very consistent (Amel flips) Suspect varies 51-71% (20% window)

Sheet Stain 2 Mom and Dad and Daughter at 80% PHR Support at 10 loci

Sheet Stain 2 Mom and Dad at 90% PHR Support at 4 loci (plus Amel flips Major/minor)

Sheet Stain 2 Mom and Dad and Daughter at 90% PHR Still support at 10 loci

Sheet Stain 2 Answer Hp – – 11 of 15 loci show support at 80% PHR – 10 of 15 loci show support at 90% PHR Hd – – 9 of 15 loci show support at 80% PHR – 4 of 15 loci show support at 90% PHR I’m going with the Daughter “really there” The mixture is Mom and Dad and Daughter with Daughter present at 10ish% (10:10:2)

Suspect Underwear Mom and Dad at 80% PHR Support at 6 loci Major/minor flips all over the place!! Suspect varies 40-68% (28% window)

Suspect Underwear Mom and Dad and Daughter at 80% PHR Support at 14 loci Do we even need to bother checking at 90%??

Suspect Underwear Mom and Dad at 90% PHR Support at 4 loci Look at that cool flip-flop! But, it’s not in the “correct for degradation” order

Suspect Underwear Mom and Dad and Daughter at 90% PHR Support at 12 loci

Suspect Underwear Answer Hp – – 14 of 15 loci show support at 80% PHR – 12 of 15 loci show support at 90% PHR Hd – – 6 of 15 loci show support at 80% PHR – 4 of 15 loci show support at 90% PHR Is there really a question? The mixture is Mom and Dad and Daughter with Daughter present at 33ish% (10:10:10)