was identified on the victim who could be traced to a family member to albert desalvo, the man accused of being the boston strangler. but he was killed in prison before he was tried on those charge is. this famous example. may i have blue dress. the one on which a d.n.a. sample turned a he said/she said case into a presidential impeachment. d.n.a. evidence has sevenned a number of important roles in high profile cases and in every day crime as well. i will talk more about that. what are we looking at when we try to identify people from their d.n.a.? we use something called a short tandem repeat. i'm illustrating that here. here is part of a sequence. part of the sequence, c.a.g.a. is repeated over and over again. that is why it is called a tandem repeat and it is a short one, it is only four bases. these repeats tend to bury in their number from individual to individual. -- vary in their number have individual to individual. on the copy of chromosome five that i got from my mother i might have five repeats. on the copy from my mother i might have two. if f. you compared hank's d.n.a. a