As criminal cases have become more complicated, Japan's law enforcement officials are promoting the use of more sophisticated technologies, such as DNA analysis, in the course of criminal investigations in order to verify facts with objective evidence. The primary DNA analysis method employed by law enforcement officials is short tandem repeat (STR) analysis, a method for identifying individuals utilizing individual differences in the number of repeat units of characteristic DNA sequences. Presently, STR analysis can discriminate between individuals with the probability of one in approximately 4.7 trillion, even when the DNA profile is the most common type among the Japanese population. In every prefectural police department, members of criminal investigation laboratories, who were trained and certified by the Training Center of Forensic Science at the National Research Institute of Police Science, perform STR analysis. Forensic DNA analysis plays an important role not only in criminal investigations but also following large-scale disasters, to aid in individual identification. The accuracy of DNA typing is increasing with the availability of STR typing kits that can examine more loci than conventional kits. However, it remains difficult for DNA analysis to identify individuals with only small amounts of samples, old samples, or mixed samples. New methods for handling these problematic samples are required. Here, we review current investigative techniques and challenges of DNA analysis, and focus on the latest research for solutions to these challenges.
Keywords: DNA typing; forensic analysis; individual discrimination; short tandem repeat.