to find out, detective mark woodman came up with an idea that changed the course of the investigation. he told analysts to test the syringe caps found in michelle's trash. >> i can remember seeing medical staff hold needle caps in their mouth while they were giving an injection, and i thought that there was a potential there for saliva dna. >> i thought that was rather brilliant, in fact. >> dna analysts swabbed the needle caps and found biological material. >> on the needle cap or cover, there was an unknown male dna profile. >> and scientists also found dna inside the syringe. >> i was able to determine that miss herndon's dna was present in one of them. >> proof it had been used on michelle. michelle's death was now classified as a homicide. and the murder weapon was propofol. >> i've never seen a propofol-related death. ever. >> but who wanted michelle dead? i wake up in the morning with no back pain. i can adjust it if i need to...if my back's a little more sore. and by the time i get up in the morning, i feel great! if you toss and turn at night, have back pain ... ... or wake u