>> all of it gone due to a simple clerical error. >> when anyone retires, you get a list of evidence on cases. there's a box. you either check dispose or retain, and the box was checked dispose for this case. >> i mean, what's that moment like when you're trying to solve this case, only to find out that physical evidence has been destroyed by your own police department? >> well, i was pretty upset. i was pretty mad. okay, to be honest, i was really mad. >> the most important piece of evidence, though, was that blood drop which was stored separately. the defense would want their own experts to test it. so if it was missing, too, the case against hansen might well be over. was that kind of a, "oh, my gosh, what if this has been destroyed, too? " >> yes. >> because then you're kind of done. >> i was stressed. >> i met with alana williams, the forensic scientist. she