How Handwriting Analysis Works

Analyzing a Sample

Partial results of handwriting analysis in Lindbergh kidnapping case
Partial results of handwriting analysis in Lindbergh kidnapping case
Photo courtesy FBI

­Analyzing handwriting is a long, careful process that takes a lot of time and, under ideal circumstances, a lot of comparison samples, or exemplars - documents that have a known author. It's not a matter of looking at two documents­ and saying "Hey, they both have a 'B' with a downstroke extending below the line - same author!" In the case of the Lindbergh kidnapping in 1932, the police had a slew of questioned documents- in all, the kidnapper sent 14 notes to Lindbergh with ransom instructions. Handwriting analysts had no problem determining that all of the ransom notes were written by the same person. But pre-existing exemplars from the main suspect, Richard Bruno Hauptmann, were scarce, so the police had to get samples from Hauptmann in the police station by way of dictation. From those requested exemplars, handwriting analysts determined a match.

­However, the police officers' methods of obtaining those samples has since been called into question - Hauptmann was forced to write for hours and hours until he nearly passed out from exhaustion. He was also told how to write, and he was shown a ransom note and told to copy the handwriting as best he could, to name just a few of the major no-nos. This of course means that the validity of the determined handwriting match is in question, and Hauptmann's execution makes a re-test impossible. There are now strict rules in place about how police should obtain a requested exemplar.

Good, untainted, numerous exemplars make handwriting analysis far more reliable than a simple one-to-one comparison. While every person's handwriting is unique, no one person writes exactly the same way twice. There are natural variations in a person's writing within a single document. Having, say, 10 questioned documents and 10 exemplars from a suspect assures that not only will the words and letters in the questioned documents show up in the exemplars, but also that almost all of that suspect's individual characteristics will appear in both sets of samples if the suspect is indeed the author of both.

The process of professional, forensic handwriting analysis is all about thoroughness. An analyst will use a magnifying glass and sometimes even a microscope in the comparison process. An analyst is looking for a wide array of individual traits:

  • Letter form - This includes curves, slants, the proportional size of letters (relationship between size of short and tall letters and between the height and width of a single letter), the slope of writing and the use and appearance of connecting lines (links) between letters. It's worth noting that a person may form a letter differently depending on where the letter falls in a word - beginning, middle or end. So an analyst will try to find examples of each letter in each placement.
  • Line form - This includes how smooth and dark the lines are, which indicates how much pressure the writer applies while writing and the speed of the writing.
  • Formatting - This includes the spacing between letters, the spacing between words, the placement of words on a line and the margins a writer leaves empty on a page. It also considers spacing between lines -- in other words, do strokes from words on one line intersect with strokes in words on the line below and above it?

With these traits in mind, we'll take a look at one common method of comparison in which the analyst begins with the first letter in the first word in the questioned document and starts building a table. To illustrate the process, we'll perform a simulated comparison using a questioned document and an exemplar each consisting of a single sentence - a nightmare for determining a definite match or non-match in the real world, but perfect for our purposes.

Questioned document Questioned document
Questioned document
Exemplar provided by "suspect" Exemplar provided by "suspect"
Exemplar provided by "suspect"

At first glance, the two samples do not appear to be different enough to automatically declare that they were written by two different people. And on closer examination, they actually appear to be quite similar. So we're going to build a table that catalogs each varied form of every letter that appears in the questioned version of this sentence. If we get to an "a" that looks exactly like an "a" we already have in our table, we skip it. We simply want each different formation of "a" in the document in our table, taking into consideration letter formation, linking strokes, spacing and other traits. In forensics, they would "copy" each letter form using a digital camera, but we're going to do it by hand. They would also make separate tables for uppercase and lowercase letters. But we're going to simplify, since this is only an example of the process of determining a match or a mismatch and not a professional or accurate comparison.

Next, we're going to make the same kind of table using the exemplar:

Finally, we're going to compare the tables and see if we have a match for each questioned-document letter form in the exemplar. Since our document consists of a single sentence, we don't have many instances to choose from. Under normal circumstances, we would have an array of potential matches for each letter form, and we'd want to find a good match in the exemplar for every letter form occurring in the questioned document. For simplification purposes, our third table is going to consist of a side-by-side comparison of our two initial tables, although an expert analyst would probably create a third table showing the exact words in each document that make up each letter-form match.

Questioned (left) and exemplar tables Questioned (left) and exemplar tables
Questioned (left) and exemplar tables

While this analysis would definitely not hold up in court due to its extremely limited scope (and sadly inaccurate letter copying), it nonetheless seems we have found a match in the exemplar for each letter in the questioned document. The same person probably wrote both sentences.

But what if the writer of the exemplar was trying to copy the handwriting in the questioned document? The problem of simulation is a difficult one in handwriting analysis. Simulation occurs when a person is either trying to disguise his handwriting to prevent the determination of a match or to copy someone else's handwriting to encourage the inaccurate determination of a match. While simulation makes an accurate analysis far more difficult (and sometimes impossible), there are certain traits that professional analysts look for to determine whether a handwriting sample is the result of simulation. These include shaky lines, dark and thick starts and finishes for words and a lot of pen lifts, all which come from carefully, slowly forming letters instead of writing quickly and naturally.

Mickey Mantle's known signature is on top; the FBI determined that the bottom two signatures are forgeries. Note the shaky line quality and variations in the starting and ending strokes. Mickey Mantle's known signature is on top; the FBI determined that the bottom two signatures are forgeries. Note the shaky line quality and variations in the starting and ending strokes.
Mickey Mantle's known signature is on top; the FBI determined that the bottom two signatures are forgeries. Note the shaky line quality and variations in the starting and ending strokes.

Simulation is just one of the factors that can foil an accurate handwriting analysis.