CLPEX Chat Board

I've heard it stated if you had a latent print with only 1 point of minutiae you could call it an id because of the rarity of such a situation.

What if you only had four and the rest was an open field? Can you still call it a match.

I have a delima. I have a latent print that measures aprox. 1/2 by 1/4 in. It has two inner most recurves, free of appendages and no rods or spikes in the center. To the right at about 2:00 are four clear points. They are not amazing, such as a short ridge or an island, just ordinary bifurcations. The rest of the print; above, below and to the left of the core are void of any points for comparison. From the first visable point on the right to the end of the print on the left I can count 20 ridges free of any level 2 detail. There is no level 3 detail to help. It is the only print in a drug possession case.

How much weight would you give the open field? Is it enough to over come such a low number of minutiae? Would you pass on it and call it a no id or would you report it as insufficient? It can still be used for elimination. If I was to call it an Id, would it be interperted as possible probable because it did not meet some arbitrary number?

I know there was a print made without any level 2 but that print had plenty on level 3 detail.

I would like any input or insights before I write the report. I can e-mail the print to anyone who wants to see it (chaterd or uncharted pairs) just shoot me an e-mail. I'm listed in the IAI directory.

Regards,
Sandy

My understanding of the premise regarding only a single ridge characteristic (generally understood to mean a level 2 feature) being capable of establishing individuality, has been that it could apply if both prints were complete prints (as in rolled). Your print would not seem to meet that criteria.

However, a second proposition remains: "Show me the prints!" (as you have offered to do).
Regards, RLT

Great question.

I would recommend reading Osterburg, et. al. and Sclove's probability model papers. Osterburg is the first to deal with open ridge systems. But the answer there will not be definitive, merely give you some sense of weighting.

Neumann's FSS model (the one demo'd at the last IAI) does address this issue and could calculate Likelihood Ratios based on open ridge systems and a number produced from such a model could help guide your decision making. This is an argument I have made before; that even if the profession chooses to not go into court with probabilities anytime soon, these models/software packages would be like a "consultation" with "another examiner" (except this one is going to provide you with a number that can be weighted into your final evaluation stage).

I will contact you offline too to discuss more so that my next statements won't show up in court, taken out of context, by an attorney (as in the past...)

g.

Sandy,

I'm sorry to do this, but my answer has to be "show me the prints".

I would also add this though.
You state that a system of 20 ridges coursing around a core consisting of a plain staple without endings or bifurcations has no 2nd level detail
If you look at level 2 as the traceable path of the ridges then your open field suddenly contains a whole lot of 2nd level detail.
You could even quantify L2 detail as the total length of all the ridges (as if you could straighten them out and lay them end to end) then, comparing that with values from known id's, give yourself an indication of how much weight to assign to your open field.

Spoken like a true Ashbaughian Ridgeologist, David, but I am having a great deal of trouble wrapping my mind around this concept of "measuring" ridges as a way of defining Level 2 detail. Can't pressure and distortion change the measurement? And even worse, if you start your measurement at the edge of the visible part of the latent print, what indication do you have where the ridge actually starts? Is it one millimeter off the edge of the latent print, or ten? If Sandy has a full "open field" that extends from one side of the latent to the other, then your "measurements" are wrong on both ends and thus, in my opinion, those measurements are worse than meaningless. I fully support the value of an open field in analysing, comparing, and evaluating a latent print. But I cannot grasp this idea of "measurements."

I am not trying to be facetious, but I wish somebody would explain this new ridgeology to an old dinosaur like me.

Thomas,

If you can see the pores (and I have no idea if you can in this case or not, since I haven't seen the print), you would "measure" in ridge units (which will remain constant), not in millimeters (which can change due to distortion).

Thomas,

Basically we are looking for a way to appreciate the quantity in our quantitative/qualitative analysis. One simple way to do this is, as Sandy has, to look at the area or size of the latent. However this does not take into account that some fingers have coarser ridges and therefore less ridge/sq in. than others. An even better way would be to count the number of ridge units, but if you can do this your open field gets its weight from the level 3 detail within it and not so much from its size.

I am not suggesting that you go so far as to get out a pair of dividers and a ruler and say that latent 'A' has 3.76 inches of ridge in agreement with the inked 'B'. More simply, by approaching level 2 detail as an "amount of ridge path" rather than as a number of Galton details, an examiner may gain over time an understanding of the weight that can be assigned to an open field.

I think I'm going to blame the English language for this one.

When talking about quantity in 2 dimensions, I can talk about size or area , and these two words convey different meanings.
In one dimension I only have the word length which conveys the meaning of a measurement.

I hope you know what I mean by this...

Puppy is to dog as kitten is to ***

Now try this one...

Area is to size as length is to ????????

and you should see what I mean.

____________________________________________________________

PS. Heidi jumped in while I was writing this and, just like a woman, got it done in far fewer words than I could.
____________________________________________________________

PPS. Sandy, please send me a copy of the uncharted prints to the email in my profile. Thanks.

Dear Heidi & David,

Thank you for your replies, but I still don't see where "measurement" by counting ridge units adds much to our arsenal of tools. In the first place, considering the "open field" question, if all of the ridge units are clear and distinct in the latent print, then a Level 3 identification is most probably possible. If the ridge units are not distinct and clearly defined, then "measuring" becomes impossible anyway.

The vast, vast majority of identifications I make are made by comparing Level 2 details (dare I use the now-hated word "Points?") Level 1 is mostly for exclusion. Level 3 details sometimes tip the scales when the points themselves don't quite get me there.

Of course, ridge texture and ridge width are part of the overall image and carry weight for exclusion or identification. I guess that is Level 1 and Level 3, depending on how you use it.

But I still question how often you would "measure" the ridges, especially by counting ridge units or even in a related manner, and reach a conclusion that you couldn't have reached by comparing patterns, points, and Level 3 (sweat pores and bumps). I liked Ashbaugh's early works, but I think he is getting a little too esoteric in his old age (what am I talking about? I'm about that age, both in years and in time in grade).

I remember seeing a Zero Point latent print identification in the JFI a few years back -- open field with lots of level 3 detail. Back to Sandy's question, "show me the print." But if you look at it and "know" it's an identification, then the issue is not one of how do you make the ident, but how do you defend the identification in court. I don't think "measurement" would be the way I would testify.

Ok say you have a latent with an open field like this
___
____
__
___
____

Right short ridges in sequence but not a lot of weight cause the ridges are short and you might just be missing a "point"

Now take

_____________________________
______________________________
_____________________
________________________________
_______________________________

Something like that would get more weight that the first.... You havent measured in cm or ridge units but you do look at how much they have in common... will it be enought... goes back to training and experiance right.

The lenghts of the ridges should not vary that much as most distortion takes place between ridges not along them.

You are not going to take a ruller to the print but and there will not be a magic number of mm's that will give you an ident

To further David J's example contrast the two following diagrams
___________
___ ______
_____/______
_______ __
_______\_____

And
___________________________________
___________________________ ______
_____________________________/______
_______________________________ __
_______________________________\_____

Once you have the boundaries of your open field defined by "points in agreement" on at least one side its value increases. And once the open filed's size is defined on all sides does it not increase more?

We are still talking about a relativistic measurement rather than any sort of numbers game and only your experience can tell you how much weight to give any ridge formation.

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On the subject of the zero point ident from the JFI.
This again depends upon how you interpret levels of detail.

IIRC the print had half a dozen or so ridges coursing almost straigh across with no curve. but there were also several broken incipient ridges.
As the definition of an incipient ridge is somewhat arbitrary then couldn't you say that the ends and dots of the incipients were "points"? I certainly took account of their arrangement and relative positions when comparing the print.

Would This Work

1. Take the latent print and piece of clear plastic. Place the plastic over the latent print and mark the core.
2. Then outline on the plastic the area of the latent print that has the open field that is free of any points.
3. Select 25 (or 50 or 100) similiar loops (same direction, approximate ridge count, from same sex, etc.) and with your overlay put in on the area you marked as the core and then count the number of points in that area that is outlined.
4. Add the numbers and divide by the number of patterns considered.
5. Would the resulting number give you some type of weight to the question at hand.

If your latent print has 4 points and your exercise aveages out to 2 points then you have an idea how many ridge characteristics would occupy the same area.

What if the exercise averages out to 5.2 points and you have 4 regular points, then your open field would have more weight than your associative minutia?