An RNA expression method for aging forensic hair samples.

A common limitation to most forensic trace evidence analysis is the ability to determine the time at which the evidence was deposited at the crime scene. This issue of timing is vitally important as it may not only reveal when the crime occurred, but could exclude potential suspects from the investigation. Using a reverse transcription quantitative polymerase chain reaction (RT-qPCR) assay, we monitored the relative expression ratio (RER) of two different RNA species (18S and β-actin) in hair samples that were aged naturally over a period of 3 months.