Persistence of DNA deposited by the original user on objects after subsequent use by a second person

doi:10.1016/j.fsigen.2013.10.005

Forensic Science International: Genetics

Volume 8, Issue 1, January 2014, Pages 219-225

https://doi.org/10.1016/j.fsigen.2013.10.005 Get rights and content

Abstract

There is a paucity of data regarding the persistence of DNA from prior user of an object after, its use by another person. To acquire a greater understanding of persistence we performed controlled, experiments encompassing over 179 objects that had only been used by one individual for an extended, period before used by a 2nd person for various but known duration. Our findings show that the profile, percentage contribution of the 1st user relative to the 2nd user of an object declines in a linear manner, over time. The retrieval of the profile of the initial user of the object is dependent on the type of, substrate and use of the object. When considering a hard non-porous object the 1st user's profile, percentage contribution drops ∼50% immediately upon use by a 2nd person and drops to ∼15% after, 90 min. When considering a soft porous object the 1st wearer's profile contribution remains, higher than that of the 2nd wearer during the first 10 h of wear by the 2nd wearer and still, accounts for ∼12% after 96 h. This substrate associated difference was also observed in an, assessment of a wide range of personal objects used by 2nd users for different durations. Particular, areas of certain objects were more likely to retain a greater proportion of the 1st user's DNA than other, areas. Alleles of unknown source were present on the majority of objects but rarely exceeded 10% of, the total profile. Greater knowledge of persistence will inform investigators regarding the likelihood of, detecting a profile of a particular individual based on the type of object and its history, and assist with, identifying the best areas of an object to target for DNA sampling.

Introduction

Crime investigators regularly encounter exhibits that have been used/worn for an extended period of time by one person (usually the owner) then subsequently used/worn by a second person. The time that the second person uses/wears the object could vary enormously, from a brief moment to an extended length of time. The DNA profile of the last user/wearer of an item is often retrievable from a touched item [1], [2]. Whilst it is frequently the last user that investigators are interested in, sometimes it is the previous user that is the focus of attention. Examples of this can include: identifying the owner of a stolen item; identifying a prior user of a weapon that may have been shared; seeking confirmation of scenarios relating to criminal activity involving a specific individual who may have used a specific item (i.e. clothing, weapon, tool equipment, keyboard, phone) or come into contact with a particular surface (i.e. door, window, furniture) which is known to have been used/touched by others since. When evaluating the chance of obtaining an individual's profile from a particular exhibit with a given history, it is valuable to understand the persistence of DNA on such exhibits. This knowledge is relevant for sampling prioritisation and targeting, as well as interpretation of profiles in case investigations. In this context an important question is: to what extent can the DNA profile of the former user/wearer of an object still be detected after use by a second person? Knowledge of persistence in given circumstances may also provide an indication of the time that has lapsed between events.

It is well accepted that biological samples collected from certain surfaces often provide a mixture of profiles [1], [3], [4], [5], [6]. This is particularly true when the target samples are of a trace nature. In such situations the underlying DNA (often also present in trace quantities) constitutes a higher proportion of the DNA sample collected. Examples include assaults where the victims’ clothing has been touched, steering wheels of stolen cars, and personal objects, such as wallets, handbags, watches, jewellery that have been stolen, and weapons owned by an individual that have temporarily been used by someone else.

There have been very few studies examining persistence of biological samples [4], [7] and even fewer that focussed on the persistence of DNA left by touch/skin cells, especially after the object has been used/worn by a second person. One such study showed that the majority of profiles recovered from wallets stolen in a simulated robbery were mixtures, with the ‘robber's profile comprising the major component of the mixture or was the single source in 40% of profiles [8]. The authors concluded that such knowledge of trace evidence characteristics of DNA will aid in its interpretation and presentation in criminal trials.

Transfer of DNA from touched objects is dependent on the substrate on which the biological material resides, the substrate the deposit area comes into contact with, the freshness of the deposit and the manner of contact [9]. There appear to be other factors, however, also influencing transfer [10]. The value of an awareness of transfer rates given particular situations to help judge the relative probability of alternative multi-step transfer events has also been illustrated [11].

Here we aim to acquire a greater understanding of the persistence of DNA deposited by the initial user on objects after various durations of use of the item by a second person. Three separate tests were conducted: Test A relating to a handled object that had a non-porous, hard, flat surface (represented by pens and pen lids); Test B relating to a worn object that was porous (represented by bracelets made of elastic fabric); and Test C, where unlike Tests A and B where all the starting objects were the same, we examine a wide range of everyday personal objects of different substrates, shapes, sizes and uses. All Test A and B replicate objects had similar determinable amounts of DNA deposited on them by an initial known single individual, while the objects used in Test C had varying unknown amounts of DNA, each from a different initial depositor. All objects from Tests A, B and C were given to a wide range of second users who used them for different periods of time.

Section snippets

Test A

Fifty-four new pens (Classic Fine blue ink, Bic Australia) hexagon shaped hard smooth plastic with a cone shaped hard smooth plastic lid taken directly from a new box were cleaned with 0.05% hypochlorite and 70% ethanol. Five pens, with their lids, were retained as negative controls and all other pens were placed together in a single large envelope. To ensure that, as much as possible, an approximately equal amount of DNA, from a known single donor source, was placed on each pen they were

Test A: pens and lids

All five negative control pens and their corresponding lids gave negative quantitation values and did not contain any allele when profiled confirming that the pens and lids used in this study were DNA-free before handling.

The five deposit control pens and their corresponding lids yielded an average of 3.394 ng (range: 4.20–9.955 ng; S.D.: 0.638) and 0.394 ng (range: 0.267–0.540 ng; S.D.: 0.118) respectively. Each pen and lid returned a full profile of the 1st user. One of the pens had one

Discussion

All 6 pens that had been rubbed between hands by the 2nd user and excluded from the comparison of pens based on their duration of writing use, gave DNA yields higher than the deposit control pens, with the 2nd user's profile completely replacing that of the 1st user in 3 of these pens. This replacement of the 1st users’ DNA is consistent with finding of Goray et al. [9] relating to the transfer of DNA when touching hard non-porous substrates in a manner where friction is involved.

It is

Conclusions

The degree of persistence of DNA from a prior user of an object depends on the type of object, the substrate it is made of, the area of the object targeted for sampling and the duration and manner of contact by a subsequent user. Alleles of unknown sources should be expected to be observed as a very minor component of the profile generated from handled objects.

Greater knowledge of persistence will inform investigators regarding the likelihood of detecting a profile of a particular individual

Acknowledgements

We would like to thank the volunteers who participated in this study and Dr Kaye Ballantyne for assistance with the preparation of the figures.

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Persistence of DNA deposited by the original user on objects after subsequent use by a second person

Abstract

Introduction

Section snippets

Test A

Test A: pens and lids

Discussion

Conclusions

Acknowledgements

Forensic Sci. Int. Genet.

Forensic Sci. Int. Genet.

Forensic Sci. Int. Genet. Suppl. Ser.

Leg. Med.

Leg. Med.

Forensic Sci. Int. Genet. Suppl. Ser.

Forensic Sci. Int. Genet.

Forensic Sci. Int. Genet.

Leg. Med.