Trace Evidence Scrapings:
A Valuable Source of DNA?
Stacy L. Stouder
Biologist
DNA 1 Unit
Kimberly
J. Reubush
Examiner Trainee
Trace Evidence Unit
Deborah L. Hobson
Examiner
DNA 1 Unit
Jenifer L. Smith
Unit Chief
DNA 1 Unit
Federal Bureau of Investigation
Washington, DC
Abstract.......Introduction.......Materials
and Methods
Results
and Discussion.......References
Abstract
Collection and analysis of
trace evidence (e.g., hairs and fibers) from evidentiary materials
may indicate an association with a suspect, a victim, or both
to the evidence. The collected trace evidence debris may also
contain sufficient cellular material removed from an item to
permit identification of the wearer of that item through DNA
analysis. To test this hypothesis, T-shirts and hosiery were
worn by FBI Laboratory personnel for a period of time and then
scraped for trace evidence. The pillboxes used to collect the
scrapings were swabbed with applicators moistened with sterile
water and processed alongside a friction swab of the item. The
amount of DNA obtained from trace evidence scrapings was compared
to the amount of DNA obtained from a friction swab of an item.
Samples were then amplified by the polymerase chain reaction
(PCR) using the AmpFlSTR® Profiler Plus Amplification
Kit (PE Applied Biosystems 1998), and the results were compared.
This study demonstrates that trace evidence debris can provide
a sufficient quantity and quality of DNA to potentially identify
the wearer of an item.
Introduction
In general, evidence from violent crimes submitted
to the FBI Laboratory is currently processed for trace evidence,
screened for biological fluids and tissues, and then analyzed
by DNA typing methods, if appropriate. One method of trace evidence
collection in the Laboratory involves scraping items to remove
hairs, fibers, and other debris adhering to the item. Because
skin cells are constantly shed, it is likely that the collected
debris contains cells from the individual who wore the garment.
These skin cells contain nuclear DNA and may have evidentiary
value for DNA analysis. Minute amounts of biological material
may yield sufficient quantities of DNA. For example, in a study
of dandruff and its potential use in forensics, investigators
found that 11.5 mg of dandruff yielded 3040 ng of
DNA (Lorente et al. 1998). Studies show that limited quantities
of DNA are sufficient to obtain a profile from several polymorphic
short tandem repeat (STR) loci (Moretti et al. 2001). Thus, skin
cells obtained from scraping an item of clothing could contain
sufficient DNA to potentially determine the source of the wearer
by STR analysis (Budowle et al. 2000).
In a bank robbery, for example, when only
masks or gloves are recovered, cellular debris may be the only
biological material available for forensic DNA analysis. Currently,
evidentiary items that have been previously screened for trace
evidence are swabbed to collect DNA from skin cells or cells
present in saliva or sweat along friction ridges (i.e., collars
and cuffs) or other surfaces where cells may be deposited (i.e.,
mouth and nose areas of a ski mask). However, substantial cellular
debris may be removed during the scraping process prior to the
item being analyzed for DNA evidence. In this study, the amount
of DNA recovered and the resulting DNA profile from the pillbox
scrapings from an item of clothing to that obtained by swabbing
the garment were compared.
Materials and Methods
Eleven employees wore a freshly laundered
item of clothing, with the exception of one participant who wore
new panty hose, for a period of time, generally one day. Females
wore hosiery, and males wore T-shirts. After the workday, the
items were collected and stored in clean paper or plastic bags
and were maintained at room temperature until analysis. All items
were processed for trace evidence by scraping the inside and
outside of the items, which were hung from a metal rack over
a table covered in clean paper. Debris was collected, transferred
to, and stored in a pillbox. The processing room was cleaned
with Cavicide® (Micro-Aseptic, Palatine, Illinois), and the
collection paper was changed after each item was scraped to avoid
potential contamination among items (FBI Laboratory 2000; SWGMAT
2000).
DNA analysis was performed on the items, along
with their corresponding pillboxes containing the trace evidence
debris, for all study participants, their cohabitants (primarily
spouses), if appropriate, and the personnel conducting scraping
and DNA analysis (FBI Laboratory 1999). Potential cellular material
was collected from each item using a sterile swab moistened with
sterile water. Full-length panty hose were swabbed on the inside
trunk and foot areas, knee-high nylons were swabbed entirely
on the inside and outside, and T-shirts were swabbed around the
neckline. Hereinafter these are referred to as friction swabs.
A second set of swabs was used to collect the material found
on the inside of the pillbox (excluding any hairs and fibers).
Following an organic extraction (Comey et al. 1994), DNA was
quantified using the human specific slot blot hybridization assay
ACES Human DNA Quantification Probe Plus Kit (Life Technologies,
Gaithersburg, Maryland; Budowle et al. 1995). Samples were amplified
using the AmpFlSTR® Profiler Plus Amplification Kit
(PE Applied Biosystems, Foster City, California) and typed by
capillary electrophoresis on an ABI Prism 310 Genetic Analyzer
(PE Applied Biosystems, Foster City, California; PE Applied Biosystems
1998) using the GeneScan® and GenoTyper® software.
Results and Discussion
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Figure 1.
The quantity of DNA recovered from friction swabs of an item
and pillbox swabs. Item 1 was worn on multiple occasions, which
may account for the increased level of DNA recovered from that
item. Note that the knee-high nylons (Items 5, 6, and 8) yielded
a minimal amount of DNA from both the friction and pillbox swabs.
Click here to view enlarged image. |
The results of this study demonstrate that DNA recovered
from friction swabs and trace evidence debris may contain a suitable
quantity and quality of DNA to conduct DNA analysis. However,
for 9 of the 11 item pairs analyzed, the quantity of DNA recovered
from the pillbox swab was equal to or greater than that from
the friction swab (see Figure 1 and Table 1). The average amount
of DNA recovered was approximately 4 ng from the friction swabs
and 21 ng from the pillboxes. In this study, on average, more
DNA was recovered from T-shirts than from hosiery, with knee-highs
yielding the least quantity of DNA. One of the T-shirts was worn
on several occasions without laundering (Item 1). Not surprisingly,
the quantity of DNA recovered from this item (100 ng from the
pillbox) exceeded the DNA recovered from the other T-shirts in
this study (20 to 40 ng).
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Table 1. Quantity of DNA Recovered
From the Friction Swab of an
Item Compared to the Corresponding Quantity Recovered
From the Trace Evidence Debris Collection (Pillbox)
Item
type/ID |
Collection method |
Friction swab |
Pillbox swab |
# of donors1 |
Source of DNA |
DNA
(ng) |
# of donors1 |
Source of DNA |
DNA
(ng) |
Major |
Minor |
Major |
Minor |
T-shirt |
|
1 |
2 |
Wearer |
Spouse |
20.55 |
2+ |
Wearer |
Spouse |
100.55 |
3 |
3 |
Wearer |
Spouse,
unknown |
< 1.55 |
1+ |
Wearer |
|
20.55 |
7 |
1 |
Wearer |
|
2.55 |
1+ |
Wearer |
|
40.55 |
10 |
1 |
Wearer |
|
2.55 |
2+ |
Wearer |
Spouse |
20.55 |
Average/T-shirt |
6.25 |
Average/pillbox |
45.55 |
Hosiery |
|
2 |
3 |
Wearer, spouse |
Unknown |
2.55 |
1+ |
Wearer |
|
20.55 |
4 |
2 |
Wearer |
Spouse |
2.55 |
2+ |
Wearer |
Spouse |
20.55 |
Knee-highs |
|
5 |
3 |
Wearer |
Spouse, unknown |
1.55 |
Insufficient profile |
6 |
4+ |
Wearer |
Spouse, unknown |
< 1.55 |
3+ |
Wearer |
Spouse, unknown |
< 1.55 |
8 |
3+ |
Wearer |
Spouse, children?2 |
4.55 |
3+ |
Wearer |
Spouse, children?2 |
1.55 |
Hosiery |
|
9 |
1 |
Wearer |
|
2.55 |
1+ |
Wearer |
|
10.55 |
11 |
2 |
Wearer |
Unknown |
2.55 |
1+ |
Wearer |
|
4.55 |
Average/hosiery |
8.55 |
Average/pillbox |
2.55 |
Average for friction swab collection |
3.55 |
Average for pillbox
swab collection |
21.45 |
1Number of donors determined
by number of alleles per locus. Peak height (in relative fluorescence
units) information also used.
2Although
the spouse and children cannot be excluded as potential contributors
to these mixtures, they cannot account for all the non-wearer's
DNA present.
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Figure 2.
Single-source DNA profiles obtained from DNA extracted from the
friction swab of a T-shirt and a pillbox swab of trace evidence
debris. The top panel (Q7-1) represents the profile from the
friction swab, whereas the lower panel shows the profile from
the pillbox swab. x = size in base pairs; y = relative
fluorescence units. Click here to view
enlarged image. |
|
|
Figure 3.
The results from Item 11, which was a new pair of panty hose,
show a mixture from the friction swab (upper panel) and a single-source
profile from the pillbox swab (lower panel). These findings suggest
that the additional type may have originated from the manufacturing
site or the wearer's environment. x = size in base pairs;
y = relative fluorescence units. Click
here to view enlarged image. |
|
|
Figure 4.
An example of a single-source STR profile obtained from DNA from
a pillbox containing trace evidence and a multi-donor profile
obtained from the friction swab of the same item. The top panel
(Q2-1) shows the profile of the friction swab containing DNA
from three or more individuals including the wearer and her spouse.
The second panel illustrates the single-source profile obtained
from the pillbox swab of that same item. Click here to view enlarged
image of the top two panels.) Panels
3 and 4 are the DNA profiles of the wearer and her spouse, respectively.
Click here to view enlarged image of Panel
3 and Panel 4. x = size
in base pairs; y = relative fluorescence units. |
|
A summary of the results is listed in Table 1. In
general, the STR profiles derived from pillbox debris contained
no DNA or less DNA from a nonwearer source than those profiles
from the friction swabs. Single-source profiles were obtained
from 50% of the pillbox profiles (i.e., 5 of 10; 1 item contained
insufficient DNA, and no STR profile was obtained) compared to
27% of the friction swabs. An example of a single-source profile
from both the pillbox and friction swabs can be seen in Figure
2. Unlike the donors of the other T-shirts, the donor of Item
7 is unmarried. Two of the hosiery donors (Items 9 and 11) are
also unmarried. The DNA profile from the pillbox and friction
swabs from Item 9 are from a single source (the wearer). Figure
3 depicts the STR profile results from Item 11. Whereas the DNA
recovered from the pillbox was a single source, the friction
swab contained a major (the wearer) and an unknown minor contributor.
The hosiery was removed from the original packaging and worn
for an afternoon prior to testing. During this time, the only
individual to come in contact with this item was the donor. These
results suggest that the extraneous DNA profile may have originated
at the manufacturing site or was transferred from the wearer's
environment (Locard 1930). Nevertheless, the wearer of this hosiery
is clearly identified as the major contributor of DNA in the
STR profile.
Figure 4 shows the DNA results from a married individual.
A single-source profile of the wearer was obtained from the pillbox.
However, the friction swab produced a mixture of DNA from at
least three individualsboth the wearer and her spouse are
included as contributors. In four sample pairs, a mixture was
present in both specimens. However, there was less contribution
from the minor contributor(s) (i.e., the spouse or an unknown)
in the pillbox profile than the friction swab profile. Furthermore,
there was only one sample pair in which the profile from the
pillbox was a mixture (the wearer and their spouse) and a single-source
profile was obtained from the friction swab (Item 10). In all
profiles containing a mixture of DNA, the individual who wore
the item is either the major contributor (12 of 13) or one of
the major contributors (1 of 13). To account for the minor contributors
in samples with mixtures, the cohabitants' (primarily spouses)
STR profiles were compared to the results. In most cases, these
individuals accounted for the other source of DNA in the mixture
(Table 1). Additional DNA contributors were found in some samples,
and their source remains unknown. However, all DNA Unit personnel
and the trace evidence technician participating in the study
were excluded.
This study demonstrates that trace evidence
scrapings can provide a source of material for forensic DNA analysis.
On average, the pillbox scrapings yielded greater quantities
of DNA, which increases the chance for obtaining a result and
for preserving the sample for possible future retesting (National
Research Council 1996). Furthermore, the DNA profiles tend to
be less likely to exhibit mixtures from the scrapings than from
the friction swab, which facilitates profile interpretation.
Additional studies are being conducted to test the possibility
of DNA carryover in washing machines during the laundering process
in an effort to explain the presence of cohabitants' DNA on items
of clothing.
References
Budowle, B., Baechtel, F. S., Comey, C. T.,
Giusti, A. M., and Klevan, L. Simple protocols for typing forensic
biological evidence: Chemiluminescent detection for human DNA
quantification and RFLP analyses and manual typing of PCR amplified
polymorphisms, Electrophoresis (1995) 16:15591567.
Budowle, B., Chakraborty, R., Carmody, G., and
Monson, K. L. Source attribution of a forensic DNA profile,
Forensic Science Communications [Online]. (July 2000).
Available: www.fbi.gov/hq/lab/fsc/backissu/july2000/source.htm
Comey, C. T., Koons, B. W., Presley, K. W.,
Smerick, J. B., Sobieralski, C. A., Stanley, D. M., and Baechtel,
F. S. DNA extraction strategies for amplified fragment length
polymorphism analysis, Journal of Forensic Sciences (1994)
39:12541269.
Locard, E. The analysis of dust traces, Part
I, American Journal of Police Science (1930) 1:276298.
Lorente, M., Entrala, C., Lorente, J. A.,
Alvarez, J. C., Villanueva, E., and Budowle, B. Dandruff as potential
source of DNA in forensic casework, Journal of Forensic Sciences
(1998) 43:901902.
Moretti, T. R., Baumstark, A., Defenbaugh,
D. A., Keys, K. M., Smerick, J. B., and Budowle, B. Validation
of short tandem repeats (STRs) for forensic usage: Performance
testing of fluorescent multiplex STR systems and analysis of
authentic and simulated forensic samples, Journal of Forensic
Sciences (2001) 46:647660.
National Research Council, The Evaluation
of Forensic DNA Evidence, National Academy Press, Washington,
DC, 1996.
PE Applied Biosystems, ABI Prism
310 Genetic Analyzer User's Manual. Perkin Elmer Corporation,
Foster City, California, 1998.
PE Applied Biosystems, AmpFlSTR® Profiler
Plus PCR Amplification Kit User's Manual, Perkin Elmer
Corporation, Foster City, California, 1998.
Scientific Working Group on Materials Analysis
(SWGMAT). Trace evidence quality assurance guidelines, Forensic
Science Communications [Online]. (January 2000). Available:
www.fbi.gov/hq/lab/fsc/backissu/jan2000/swgmat.htm
Short Tandem Repeat Analysis Protocol, FBI Laboratory, 1999.
Trace Evidence Unit Protocol, FBI Laboratory, 2000.
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