welcome back to "dateline extra." here again is keith morrison. >> reporter: sometimes the biggest breakthrough in a murder case can come from the most unassuming clues. for detective jim wallace, it was something buried in a routine crime lab report. yanos' pants, which he washed the morning of the murder and hung up to dry in his shower again tested negative for blood. but this time the lab report noted something else found on those pants which caught the eye of detective wallace. dirt. >> if you are washing these pants, what is the goal? aren't you trying to wash the dirt out? >> reporter: you think. >> in this case the dirt was present, except there was luminol glowing. >> reporter: the chemical police