3 person example #2 suspect boxer shorts (the ladies man)

3 Person Example #2

Suspect Boxer Shorts(The Ladies’ Man)

The Scenario

• Victim accused Subject of rape in store room at a club

• But she waited 4 days to report it• She could, however, describe the “Thomas the

Tank Engine” boxers of her assailant• Investigation led to Suspect who indeed had

“Thomas the Tank Engine” boxers

The Scenario

• Accused said he didn’t do it• He said he couldn’t have done it because he

had sex with a waitress in the store room of the club that night

• The waitress said she had sex with him in the store room at the club

The Egram

Enter question text...

1. Not interpretable by our guidelines

2. Mixture of 3 people – no stat3. At least 3 people – no stat4. Indeterminate mixture, CPI5. We would exclude only6. We have a way to deal with

it including a stat

My Interpretation

• (This is the part you REALLY must do before looking at any references)

• Mixture• Consistent with 3 persons• 5 loci with nothing in the Danger Zone• The remaining loci might have drop out• Profile is interpretable and I can do a stat

The Interpretation

• Since you have 5 loci with everything above stutter, why not just do a 5 locus CPI?

4.6.3. When using CPE/CPI (with no assumptions of number of contributors) to calculate the probability that a randomly selected person would be excluded/included as a contributor to the mixture, loci with alleles below the stochastic threshold may not be used for statistical purposes to support an inclusion. In these instances, the potential for allelic dropout raises the possibility of contributors having genotypes not encompassed by the interpreted alleles.

4.6.3.1. Alleles below the stochastic threshold may be used for comparisons and/or to establish the presence of a mixture or male DNA (e.g., Y allele at amelogenin).

4.6.3.2. A restricted CPE/CPI may be applied to multiple major contributors despite the presence of minor contributor(s) alleles below the stochastic threshold; a description of how to calculate can be found in Section 5.3.5.

The Interpretation – CPI

• Cool! This one is easy

D8 D7

D16D13THO1


• 4.6.3.2. A restricted CPE/CPI may be applied• So if I have a “clear” major(s) I can also use

those loci!• Maybe you could pull out a major here

D18D21 D19


• But…. Unfortunately all those “tall” peaks match the owner of the boxers– (I peeked – we were going to “interpret without

looking at the references”)– (If we hadn’t at least looked at the

assumed/expected person/owner, we’d be in a mess)

• But we still have those 5 loci >300


• But do we really have 5 loci >300 for all alleles?• SWGDAM - loci with alleles below the

stochastic threshold may not be used for statistical purposes

• But there’s a huge hole in that


• Look at THO1• Are we positive the 9 is from a single

contributor?• If not, it’s pretty much a given that:

– Someone is contributing <300– Therefore, we have allele(s) <300– Therefore, we can’t use that locus

THO1


• Look at D13• Pretty much certain that if we correct for

stutter, 13 <300• So much for that locus• Now we’re down to 3 loci for CPI

D13

• D8 and D7 are no better• Are you 100% certain all contributors are >300?• If there are 2 contributors to the 14 (D8) and the 8 (D7) someone MUST be <300 because both are <600 rfu• (Plus the 8 is in stutter position)

D7


D8


• That leaves us with only D16 to consider• There are only 2 alleles, and we already gave

up on other loci like this for 2 person mixtures• And it’s even worse than it seems -

D16


• D16 has “ghost” peaks• So we “know” there are alleles missing here

even though all “detected” alleles are >300

• Bye, bye CPI

The Interpretation – Now what?

• RMP to the rescue!• (With one “problem” at D16)• But let’s look down in the baseline before we

decide how to move on

The Egram – Looking in the Weeds

The Interpretation – mod RMP

• Other than D16 I have no other concerns about the baseline

• By that I mean I don’t see anything that if it were “real” would change the interpretation of “consistent with 3 contributors”

• Let’s look at some spots were it could possibly be argued that’s not true, but I think it is

• D3

• 5 Alleles called• 3 more “blips”• 5 + 3 = 8 so 4 people?


1380

15.273

1048


• The 10 and 13 might be only stutter

• The 15.2 probably not

• Which would mean “6” alleles, so still 3 people

1380

15.273

1048


• Worst case scenario – 4 people for D3?

• Correct for stutter (50%) 2 “alleles” go away• Consistent with 3 people!


• So at D3, what happens if I have a reference to compare that has a 15.2?

• As long as that person’s other allele is found in the mixture there, they are still included

• Remember, I’m allowing for “Anys” so I expect drop out is possible

• I wouldn’t exclude, but would make locus = 1 for that person


• D2 is similar• Could there be an

18, 20 or 26?• 2 of those are in stutter positions• We can test it again – Do we have more than

6 alleles?


• Worst case scenario – 4 people for D2?

• Correct for stutter (50%) 2 “alleles” <20 rfu• Consistent with 3 people?


• Do I need to worry about “alleles” below 20?

• NO WAY!! So, consistent with 3 people


• So that was a really LOOOOONNNNNG discussion to say this:

• Just do a modified RMP – It covers for all the “potential” drop out here,

since any drop out would still be consistent with 3 people

– But, we have to drop D16 from the calculation– We “KNOW” there is drop out there


• The actual stat takes about 3 clicks• 1. Open the sample into the Mix Interp Window• 2. Operations>Mixture Frequency• 3. 3 contributors• 4. Open Frequency Report

• (OK, 4 clicks)

D18The Interpretation – mod RMP

• Quick look at D18• There are 3 Allele, Anys here


• Quick look at D5• There is 1 Allele, Any here


• Quick look at FGA• 6 Alleles and 3 People, so subtract homozygotes


• The Final Stat• 1 in 13,400 (1 in 462,000 if D16 kept)

Last Thought

• Remember D16?• The “ghost” alleles?• We dropped that locus for the stat

– Made it “1.0” mathematically– It’s now a “neutral” locus

• The right LR model would cause D16 to be supportive of Hd if POI were 12, 13 (the ghost alleles)

Last Thought

• But, what form of the LR?– Unrestrained combinatorial method?– F or Q method?– D method?– Semi-continuous model?– Continuous model?

• How many of us know what we mean when we say “I need LR with drop out?”

Last Thought

• We are working hard to understand those LR models

• We are moving towards a LR model that incorporates Q and D

• We want to include our phr and p information that we currently use for RMP

• This could then be considered a semi-continuous LR

Oops! We Forgot

• Is Victim included or excluded as a contributor to the three person mixed DNA profile recovered from the boxers of the Accused?

• She cannot be excluded• What about the waitress????

3 person example #2 suspect boxer shorts (the ladies man)

Documents

stat slide

club slide

person slide

egram slide

interpretation of consistent

bye cpi slide

interpretation mod rmp

interpretation cpi d16