How does forensic handwriting identification work?

Answers to your questions about the news.
March 26 2009 6:46 PM

Murder, She Wrote

How forensic handwriting identification works.

Handwriting on paper. Click image to expand.
A handwritten document

The Los Angeles District Attorney's office has convened a grand jury to probe the 1985 disappearance of John and Linda Sohus, who once rented property to Clark Rockefeller. Two handwriting experts said on Wednesday that they'd been subpoenaed to weigh in on the authenticity of a postcard, purportedly mailed from France by Linda Sohus after she vanished. What do forensic handwriting experts look at when trying to match a disputed document?

Twenty-one distinguishing characteristics. According to one standard textbook, that's the number of handwriting elements that may reliably help distinguish a person's writing. These include the dimensions and proportions of the letters, the spacing both between and within words, and the way in which words and letters are connected. (In the cursive word cat, for example, does the pen line go all the way around the circular part of the a before doubling back to complete the loop?)

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The first step in a handwriting examination is to collect "known" documents—that is, writing samples definitively penned by the person in question. Next, the examiner determines how suitable that material is as a base-line specimen. Is there enough of it? Does it show a natural range of variability? Was the writer disguising her handwriting at any point or trying to simulate someone else's? (A naturally written line will show wide variation in thickness because people tend to change speed as they write. A person trying to alter her handwriting, on the other hand, will tend to write more slowly, resulting in a more even line.) These characteristics are all taken into consideration during the following step, when the examiner compares the "known" documents with the disputed one, element by element—sometimes with the help of a software program. There's no standard level of correspondence that must be reached for a document to be declared a match or nonmatch—each individual examiner makes the call, using his best judgment.

According to the handful of studies on the subject, a trained examiner will be correct more often than a layman. One 1997 study asked both professionals and amateurs to examine 144 pairs of documents and determine whether the documents in each pair were written by the same person. Both groups were as likely to answer correctly when the documents were, in fact, a match; however, amateurs were six times more likely to declare a positive match when none existed. Nevertheless, forensic handwriting analysis is not always accepted in the American judicial system. Individual judges have the authority to decide whether the conclusions of a handwriting examination are admissible as expert opinion testimony and whether the legal team's chosen examiner is a credible expert witness.

Bonus explainer: How do you become a forensic handwriting expert? Most document examiners learn their craft through two- to four-year apprenticeships, either with government organizations such as the FBI or CIA or with private practitioners. Those apprenticeships usually involve reading the classic texts of the field, writing essays, and courtroom training, in addition to practical lab experience. Oklahoma State University offers a stand-alone program in document examination, and many forensics programs offer individual courses.

Got a question about today's news? Ask the Explainer.

Explainer thanks Robert Baier, Ron Morris of Ronald N. Morris and Associates Inc.,and Gerald B. Richards of Oklahoma State University.

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