, this horn is made of keratin, the same stuff your fingernail is made of. on the black market it's more valuable than gold or platinum. a specimen like this could sell for close to $400,000. determining the species could impact the penalty. some are more critically endangered, like black rhinos, wild. >> what are we looking at? >> the horns from the left are from a black rhinoceros, and on the right from a white. rhinoceros horns are unique. there's a big one. if you look at the base, there's not a hollow center. the skull itself has like a boney round portion and the horn sits on top of that boney portion of the skull. >> how would you determine one species of rhino from another by looking at the hornings? >> the one on the left is round in the front. you can see that. flatter. >> this one is scared off here, difference. >> what if your evidence looks like this. >> then you get carved objects, it's difficult. you do not have any other landmarks characteristic of the rhino orn. >> this is the deputy director of the lab, and runs the chemistry unit. >> there

. >> arsenic combined to keratin, which is the major protein in hair. so as the blood circulates through the body and it circulates to the root of the hair follicle, some of the arsenic will become incorporated in the hair follicle. >> when poison circulates in the body, it comes into contact with the hair follicles. so traces of the poison will remain in the hair as it grows. since hair grows approximately 1 centimeter per month, a strand of hair can identify exactly when a person was poisoned. first, debbie's hair was divided into pieces, each 1 centimeter long. using atomic absorption spectrophotometry, a beam of light is passed through each hair sample. >> when that light is absorbed, the amount of light that is hitting the detector on the other end decreases. the change in intensity of light that's reaching the detector is directly proportional to the amount of arsenic in that sample. >> the computer-generated results were startling. >> debbie started receiving small doses of arsenic in may of 1999, and towards the end of july of 1999 she received