Forensic Molecular BiologyNew DNA Methods Bring Skeletons Out of the ClosetMichael Gross

few days before Christmas 1990, 26-year-old Geraldine Palk was brutallyraped and murdered near her home inSouthern Wales. The forensic experts investigating the case at the time pro-duced DNA profiles of her attacker andcompared them with samples from over5000 men, but they were unable to finda match. In the attempt, they used up allthe DNA samples available, so there appeared to be no hope left to solve thecase. In 1995, the UK government set upthe National DNA Database, designed toaccommodate DNA profiles of all peopleconvicted or suspected of seriouscrimes, but it uses different sequencesfrom the ones in the DNA profile ob-tained in the Palk case. More than adecade later, however, investigators ofthe British Forensic Science Service(FSS, a department of the UK home office, which provides forensic servicesto police forces in England and Wales)revisited her case and analysed theseemingly empty plastic tube in whichmedical swabs had been stored. Using anew, extremely sensitive PCR approachknown as Low Copy Number (LCN)analysis, they obtained a new DNA pro-file of the attacker. Comparing the newDNA profile against the database, the in-vestigators identified a new suspect,who was then prosecuted and convictedin November 2002.

In principle, LCN profiling is just poly-merase chain reaction (PCR) run overmany cycles. However, because of theenormous power of the method to pickup even single molecule contaminants,researchers have to be extremely carefulin excluding any source of contamina-tion. Standard procedures would involvearound 1 ng of DNA and up to 30 amplifi-cation cycles (i. e. billion-fold ampli-fication). To push the procedure into the picogram range by using more than30 cycles, one has to follow specific pro-cedures. As Peter Gill, an LCN profilingexpert at the FSS explains, increasingthe cycle number too far will not result inincreased sensitivity, but only encourageartefact production. Moreover, suchhigh-sensitivity work must be conductedin a sterile laboratory. DNA profiles of allinvestigators must be compared to anyprofiles obtained.

Unfortunately, the quality of the con-clusions that can be drawn from a posi-tive result decreases as the sensitivity in-creases. For instance, if a blood stainyields a DNA profile after a small num-ber of cycles, one can be confident thatthe profile belongs to the DNA from theblood. If the blood is old and degraded,and LCN profiling has to be applied,there is an increasing risk that an invisi-ble but fresher contaminant, e.g. fromspit droplets is responsible for the DNAfound after amplification. Thus, investi-gators often have to downgrade the de-scription of their results to stay on thesafe side.

Used wisely and with awareness of itsproblems and limitations, however, highsensitivity PCR can revolutionize forensicinvestigation and shed new light on casesthat have remained unresolved manyyears ago. Taking this idea to a system-atic level, the police in the county ofNorthumberland, in the North East ofEngland, have launched the “OperationPhoenix” which aims at reconsidering allunresolved sexual offences that occurredbetween 1985 and 1999. FSS scientistshave looked at more than 200 of theseold cases selected by the police force us-ing DNA techniques such as SGMplusand LCN, which had not been availablewhen the offences were first inves-tigated. They obtained 39 DNA profiles,of which 19 could be matched to aperson included in the NationalDNA Database.

The first of these old casesgoing to court ended in January thisyear with aconviction fora rape com-mitted sevenyears earlier.FSS sources ex-pect that severalother cases from thisoperation will also goto court. More generally,an FSS specialist advisersays, “the approach used inOperation Phoenix by Northum-bria Police could now become theblueprint for other similar opera-tions.”

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BIOforum Europe 06/2003, pp 322-323, GIT VERLAG GmbH & Co. KG,Darmstadt, Germany, www.gitverlag.com/go/bioint

of the original claim, one would alsohave to scientifically prove that the maleline has been reported truthfully.)

Back in the present day, while thedouble helix makes up much of the evidence that forensic scientists look atnowadays, there are also cases where alack of useful DNA evidence forces themto turn to other materials, such as textilefibres. This happened in the case of themurdered schoolgirl Sarah Payne, whichrocked Britain in 2000 and led to a waveof vigilante action and violent attacksagainst “suspected pedophiles” (in onecase an obviously illiterate mob attackeda pediatrician instead!). While DNA evidence was important for the identifi-cation of the victim, the crucial evidenceleading to her killer came from the vel-cro fastening of Sarah’s shoe which hadtrapped 350 fibres. Investigating theseone by one under a microscope, investi-gators could attribute some of them toSarah’s clothing, and others to items ofclothing found in the suspect’s car. In thiscase, there was no DNA evidence leadingto the attacker, but a conviction was se-cured based on the analysis of the fibres.

Forensic work has the intrinsic disad-vantage that it only starts when it is toolate and somebody has been killed orgrievously harmed. However, consider-ing that in the days of PCR a single hair issufficient evidence to link a suspect to acrime, people with murder on their mindshould be aware that they are muchmore likely to be caught than they wereonly a decade ago. The widespread inter-est in forensics-based TV shows such asCSI: Crime Scene Investigation mighthelp to spread the word. Such that in thelong term, molecular biology and otherscientific methods used in forensic analy-sis might help to make our world a saferplace to live in.

Michael GrossHe is a science writer inresidence at the school of crystallography,Birkbeck College,London.

He can be contacted via his web page at www.proseandpassion.com.

Occasionally, the FSS is also consultedon cases that have remained unsolvedfor decades or even centuries. After themeltdown of the Soviet Union, they wereapproached by Russian authorities toanalyse the skeletons found in a shallowgrave in Ekaterinenberg, which were be-lieved to be the remains of the last Tsarand his family. Following extensive stud-ies of both the nuclear and the mitochon-drial DNA recovered from the bones, theinvestigators came to the conclusion thatthe bones found were indeed those of theRomanov family. The skeletons were at-tributed to the Tsar, his wife, and three ofthe five children.

In an even older murder case, the FSSresearchers analysed the blood stainsfrom the clothes in which the “wild child”Kaspar Hauser was stabbed to death inDecember 1833. He had mysteriously appeared in Nuremberg out of nowherea few years earlier. People speculatedthat he may have been the legitimateheir to the Dukedom of Baden, literallysent to the wilderness in a conspiracy tomake somebody else the Grand Duke.The DNA tests carried out by the FSS

showed that Kaspar Hauser is not related to the present day male-

line descendants of theGrand Dukes. (Note,

however, thatfor a complete

falsification