Hello Everyone,
I am in the processing of writing procedures manuals for my latent unit. We do both processing and comparisons here. Some conversation and disagreement has come up regarding how many chemicals an examiner should use during the processing of an evidence item.
For example - with porous items, I have one employee who thinks it is justified to use only DFO and ninhydrin since the remaining techniques (things like Zinc Chloride and Physical Developer) "hardly ever produce anything." I, however, don't feel that is a strong enough justification for NOT doing all that one could.
Procedures in laboratories I have consulted generally follow one of two guidelines when processing. Either...
1) They continue down the line of the recommended sequence until they develop ridge detail that appears to be AFIS quality, then stop. In their reports, they state that the process was stopped mid-sequence and that the sequence may be completed if necessary. Especially in cases where the developed ridge detail results in a suspect ID. If the Detective in charge of the case believes additional suspects may have handled the item, the lab can then continue the process to try to develop additional ridge detail
or 2) They use every single chemical they have available that would be appropriate, even if they developed AFIS suitable ridge detail in the first step. And they continue to photograph/lift the same detail after every step, later choosing the best photo/lift of each print for comparison.
I'm wondering how other laboratories handle this, and what justifications they use when explaining this decision in court.
Processing - How far do you go?
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ER
- Posts: 351
- Joined: Tue Dec 18, 2007 3:23 pm
- Location: USA
Re: Processing - How far do you go?
Our lab follows a hybrid between those approaches.
People continue through processes until they are reasonably confident (based on their experience) that further processes will not develop additional latents. So, for some items, not every possible process is used. However, with each process that is used, photographs/lifts will be taken of the same ridge detail even if it was captured with a previous technique.
We capture a version of the same latent after each technique because it can difficult to tell which version is best for comparison while capturing the images, so it's better to have more options.
We explain situations where not every process possible was used by saying that we are reasonably confident (based on experience) that further processes will not develop additional latents.
Our examiners are given a great amount of leeway on processing, and we rely on the examiners to make the best decisions. It is easier for us because we have fully trained LPE's doing the processing. Labs with evidence techs processing items would need to give less leeway in processing technique options.
Finally, in some circumstances we will contact the officer and advise that processing should be discontinued (due to ID or something else) even though additional steps could develop additional latents. For these circumstances, we let the submitting officer make the final call.
People continue through processes until they are reasonably confident (based on their experience) that further processes will not develop additional latents. So, for some items, not every possible process is used. However, with each process that is used, photographs/lifts will be taken of the same ridge detail even if it was captured with a previous technique.
We capture a version of the same latent after each technique because it can difficult to tell which version is best for comparison while capturing the images, so it's better to have more options.
We explain situations where not every process possible was used by saying that we are reasonably confident (based on experience) that further processes will not develop additional latents.
Our examiners are given a great amount of leeway on processing, and we rely on the examiners to make the best decisions. It is easier for us because we have fully trained LPE's doing the processing. Labs with evidence techs processing items would need to give less leeway in processing technique options.
Finally, in some circumstances we will contact the officer and advise that processing should be discontinued (due to ID or something else) even though additional steps could develop additional latents. For these circumstances, we let the submitting officer make the final call.
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Peter Griffin
- Posts: 74
- Joined: Mon Apr 30, 2007 3:15 pm
- Location: Quahog. RI
Re: Processing - How far do you go?
Hey bficken
I have worked at a couple labs and they each did things slightly different. At one lab they pretty much would always work a non-porous item through a sequence of ALS, CA, Dye, Powder, but for porous it was 90% just ninhydrin, with 10% being DFO and Nin. Iodine and PD were used based on the substrate and the type of case.
At the other lab, it was mostly just CA and Dye for non-porous. Porous was processed the same as above without Iodine (which is good since that is fairly toxic).
Based on my experience it was not really worth the time to look at every item under the ALS first on the off chance there is inherent luminescence. Also, the number of new prints developed with powder after the dye stain was not significant.
I think the important thing to include in any manual you are writing is to find a good middle ground of being specific, but not too specific. There are a lot of factors that will determine what you are going to do in a case. You are probably not going to spend 40 hours processing every item through an entire processing sequence for a petty burglary case. A good phrase to include in your manual is “at the discretion of the examiner”. This leaves it open for the examiner to use the processing techniques they feel are appropriate. With unlimited time and resources you would work all cases the same, but most agencies do not have that luxury.
Our manual lists all of the processes that are available but it is up to the examiner to determine the best course of action.
Hope that helps
PG
I have worked at a couple labs and they each did things slightly different. At one lab they pretty much would always work a non-porous item through a sequence of ALS, CA, Dye, Powder, but for porous it was 90% just ninhydrin, with 10% being DFO and Nin. Iodine and PD were used based on the substrate and the type of case.
At the other lab, it was mostly just CA and Dye for non-porous. Porous was processed the same as above without Iodine (which is good since that is fairly toxic).
Based on my experience it was not really worth the time to look at every item under the ALS first on the off chance there is inherent luminescence. Also, the number of new prints developed with powder after the dye stain was not significant.
I think the important thing to include in any manual you are writing is to find a good middle ground of being specific, but not too specific. There are a lot of factors that will determine what you are going to do in a case. You are probably not going to spend 40 hours processing every item through an entire processing sequence for a petty burglary case. A good phrase to include in your manual is “at the discretion of the examiner”. This leaves it open for the examiner to use the processing techniques they feel are appropriate. With unlimited time and resources you would work all cases the same, but most agencies do not have that luxury.
Our manual lists all of the processes that are available but it is up to the examiner to determine the best course of action.
Hope that helps
PG
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SConner
- Posts: 145
- Joined: Wed Mar 04, 2009 11:06 am
Re: Processing - How far do you go?
I work in an evidence processing unit although I am not a trained latent print examiner.
Our methods are similar to those explained by ER. We have a flowchart that we follow depending on if the item is porous, non-porous, glossy/coated cardboard, etc. About 95% of the time we will carry through with all of the steps listed on the flowchart. On very rare occasions we will stop before all of the steps have been completed and that is generally when we feel that we have a sufficient number of excellent quality latent prints and a supervisor trained in latent print examination gives their approval. Our report will note that processing was interrupted and that further processing may be possible. We will photograph all suitable friction ridge detail at each step, however, if the dye stain photo is much better than what we may have preserved at the visual or after CA fuming, we don't have to keep all of the prior photos.
Our methods are similar to those explained by ER. We have a flowchart that we follow depending on if the item is porous, non-porous, glossy/coated cardboard, etc. About 95% of the time we will carry through with all of the steps listed on the flowchart. On very rare occasions we will stop before all of the steps have been completed and that is generally when we feel that we have a sufficient number of excellent quality latent prints and a supervisor trained in latent print examination gives their approval. Our report will note that processing was interrupted and that further processing may be possible. We will photograph all suitable friction ridge detail at each step, however, if the dye stain photo is much better than what we may have preserved at the visual or after CA fuming, we don't have to keep all of the prior photos.