DNA exists as an invisibly thin strand in a tangled knot in the cells of the body. If straightened out, the DNA from each cell would be 2 metres long. That's more than six feet of it inside a cell invisible to the human eye!
The DNA from all the cells in the human body would stretch to the sun and back 500 times. That is more than 45,000,000,000 miles of DNA!
Profiling is the method used; certain parts of the DNA, which are known to vary widely in length between individuals, are examined. Eleven such areas are tested in the latest techniques. By comparing the profile of these lengths it is then possible to link a person with DNA from a crime scene or weapon. Profiling the whole molecule is not economical or necessary.