who killed karen pannell? stigators were taking a close look at her ex-boyfriend, roc, whose name was found scrawled in blood at the crime scene. roc admitted to having a stormy relationship with karen but insisted he didn't kill her. was there more to the bloody clue than met the eye? forensic specialist anna cox was trying to unlock what her naked eyes could not see. when she did, her discovery would send the investigation in a completely different direction. here again is dennis murphy with written in blood. >> the handwriting was on the wall and forensic specialist anna cox was intent on breaking down the key piece of evidence implicating karen's boyfriend, the three letters in blood, roc. you would spend hours looking at these letters? >> i did. >> you actually cut the sheet rock out of your place and took it into your lab? >> yes. i have to look at those letters, everything about them. >> using a high powered microscope, she did an analysis of the specks of blood that stained the wall as karen was stabbed