For over a decade, molecular biology methods have been used to resolve identity issues in violent crimes, acts of terrorism, missing persons cases, mass disasters, and paternity testing. One very sensitive method is the direct sequencing of mitochondrial DNA (mtDNA). A mitochondrion contains 2–10 copies of mtDNA, and there can be up to 1000 mitochondria per somatic cell. Because of the large number of copies of mtDNA, tissues such as hair, bones, and teeth can be typed more readily than with nuclear-based DNA markers. mtDNA sequencing is the primary genetic analysis used to identify individuals from bones recovered from American war casualties. Victim remains from the World Trade Center tragedy have had their mtDNA sequenced. In addition, mtDNA analysis has been used in evolutionary and anthropological studies, including analyses of ancient DNA.