Science in court: DNA's identity crisis

When Peter Hoe was found stabbed to death in his home in North Yorkshire, UK, in the afternoon of 13 October 2006, investigators were able to connect the murder to brothers Terence and David Reed on the basis of a small amount of DNA lifted from shards of plastic found near the body. The men were convicted the next year.

But an appeal to the ruling heard in 2009 raised questions about the reliability and interpretation of DNA profiles drawn from very small amounts of genetic material, a technique known as low-copy-number analysis. In the appeal, the Reeds' lawyers argued that Valerie Tomlinson, an officer involved in the analysis at the Forensic Science Service (FSS) based in Birmingham, UK, had overstepped her bounds by speculating how the men's DNA came to be on the pieces of plastic — thought to have broken off two knife handles. The appeal failed last December, but a larger question looms about how suspects can be fingered from such a small amount of DNA.

The case is one of the most recent public airings of...