April 08, 2020

New DNA fingerprinting

According to articles in a recent issue of New Scientist, it is going to be increasingly difficult to escape the long arm of the law in the near future. The criminal’s undoing will not be some sharp-eyed human detective who goes over the crime scene with a fine-toothed comb but robots with the ability to collect and analyze physical and chemical evidence and compare it to nationwide or worldwide databases. The latter ability will give new meaning to the old saying that, “You can run but you can’t hide.”

Eyewitness descriptions, particularly those given of suspects in high-stress situations, are typically so unrealiable they are all but useless in obtaining convictions. This may soon change, writes Bob Holmes, with the use of a technique called computerized face recognition. The system developed by Viisage Technology in Massachusetts divides all human faces into 128 distinctive features called eigenfaces. Given a composite drawing, or ideally a partial photograph from a security camera, the computer determines how many of the eigenfaces are present. It next searches a database of faces for the same pattern of eigenfaces to make a potential match. Massachusetts uses the technique to catch people collecting welfare in more than one locale while California has placed the photos of several thousand sex offenders into a database. One forensic scientist hopes all 50 states will one day have their driver’s license photographs stored in a nationwide databank that can be compared against witness’ descriptions. While this would not provide an exact match, it would generate a workable list of possible suspects.

DNA fingerprinting is proving a powerful supplement to the normal version because of its amazing versatility. DNA matches can be obtained from samples such as saliva, semen, hair and even a few flecks of dandruff. The major problem with fingerprints of both the normal and DNA variety is that current databanks are overloaded with samples. The FBI has a database of 42 million fingerprints and it can take up to four months to achieve a match. It will take several years to computerize all of these into a form that will allow nearly instantaneous matches. DNA data, which is also piling up at an alarming rate, can be matched fairly quickly with a method devised by Nanogen, a biotech company in San Diego. Before the 21st century is too advanced, it will be possible to take both types of fingerprints at the scene of a crime and the data compared to worldwide databanks for a positive ID.

There is a great deal of evidence at a crime scene other than that personally connected to the suspect. Dennis Ward of the FBI crime lab has devised a means of identifying chemical elements by examining X-rays emitted by substances bombarded with an electron beam. Each element has a characteristic emission and this allows him to find the elemental makeup of commercial substances. For instance, he has a databank of the composition of all brands and makes of duct tape often used to bind victims. A fleck of adhesive from the tape allows Ward to identify the tape. Eventually, he hopes the FBI databank will contain the elemental compositions of thousands of commercial compounds.

Two other bits of evidence often found at crime scenes are hairs and bite marks. Today, hair samples are compared under a microscope and an opinion rendered as to whether or not there is a match. These are often challenged and some courts will not even admit hair matching as evidence. A new program takes the video images of two hairs and feeds them into a computer which then compares a number of features between the two. It has had an 85 percent success rate in even its early phases. Similarly, bite marks are compared to a cast of the suspect’s teeth by an expert whose specializes in the field. Even so, any opinion is frequently called into question unless the teeth in question have some glaring abnormality.

Recently, it was learned the bacterial colonies in people’s mouths are unique to each individual. This may soon lead to a “bacterial genetic fingerprint” that will point to a single suspect.

Clair Wood is the Bangor Daily News science columnist.

Have feedback? Want to know more? Send us ideas for follow-up stories.

comments for this post are closed

You may also like