Why is 'gel electrophoresis' important for deoxyribonucleic acid (DNA) testing in criminal cases?

Gel Electrophoresis is an important technique for DNA fingerprinting because DNA is a charged molecule. DNA molecules move when an electrical field is applied to a liquid in which they are dissolved. In gel electrophoresis, the DNA sample is digested by a restriction enzyme which cuts the DNA into fragments at specific sites. The number of these sites present in an individual’s DNA dictates the number and size of DNA fragments generated by the enzymes. If the solution is simple containing water and some salts, then all the DNA molecules move at nearly the same speed. Under these conditions, it is hard to distinguish the tiny disparities in the motion of different kinds of DNA. If the solution is made less liquid, as in a gel, then all the DNA molecules start moving with different speeds. Usually, smaller DNA molecules move faster than larger ones. After a while, the molecules are separated by size and the bands of DNA appear in the gel. As DNA composition is unique for an individual, it is possible to identify the DNA of the suspect by this method.