http://www.newscientist.com/news/news.jsp?id=ns99996703
"DNA profiling has enabled us to link a suspect to a sample of blood, hair or saliva found at a crime scene. But until now, there was no way of knowing when the suspect was there - giving the guilty room to wriggle free. Now a team in America has developed a test that can reveal when a sample was deposited by measuring how quickly certain genetic material breaks down. The test measures two forms of RNA and works with as little as one microlitre of blood. The technique may even be sensitive enough to tell investigators when a fingerprint was left."
