Busting crime with digital 'wanted' posters

Busting crime with digital 'wanted' posters

It is well known that in criminal court cases, the testimony of eyewitnesses can be flawed.

As the United States Supreme Court noted in one case: "The annals of criminal law are rife with instances of mistaken identification."

A study published in the Columbia Law Review in 2008 reported that of the 200 convicted criminals proved innocent through the pro bono efforts of activist lawyers, 158 had been found guilty because of mistaken eyewitness testimony.

A common practice in crime investigations is for police artists to sketch "wanted" posters based on eyewitness descriptions.

Now, however, a better understanding of DNA markers, better software and higher computing power may deliver more accurate "wanted" posters.

In January, for the first time in the US, police in Columbia, South Carolina, investigating an unsolved double murder released a digital picture of a suspect not based on eyewitness accounts.

Instead, it was a software-generated sketch that began with genomic data derived from the suspect's DNA picked up at the scene where a young mother and her three-year-old child were cruelly murdered in 2011.

What this means is that any DNA the police may collect at a crime scene can now be used to work out what the suspect likely looks like.

This technology is called DNA phenotyping, where "phenotype" means a description of one's externally visible traits such as height, weight, hair and eye colour.

The technology focuses on the genes or portions of one's DNA that contribute to physical traits such as skin, hair and eye colours, gait, left-handedness and so on.

From this, the next step is based on the idea that people with the same geographic ancestry - that is, their ancestors came from East, South or South-east Asia, Northern or Southern Europe, and so on - are more likely to share certain genes that contribute to their phenotypes.

In the next step, face recognition software is used to make statistical estimates of how a suspect's facial features and complexion might look like, given his ancestry.

This software works against a background of data inherent in three-dimensional mugshots of known persons with the same ancestry, usually those already stored in databases of criminals with their DNA and other personal details.

So, despite its name, the technique does not actually involve isolating the genes responsible for particular traits to directly generate digital pictures of human faces.

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