it was also keary was involved.nd keary was the spark plug, if you will. >> in tracing devon guzman's last known movements, a witness told police he saw devon guzman at michelle and brandon's home on the night of her murder. >> i woke up because there was some noise outside that i realized was an argument. the woman i now know to be devon was standing on the doorstep on the house in back of me with two people inside the house, the three of them arguing. i looked at the clock. it was 12:35. >> detectives sprayed the inside of the couple's home with fluorescein, which is like luminol in that it glows when it comes into contact with red blood cells. they found nothing. >> we should be able to detect blood all over the place if this is where her throat was cut, and we go into the house, and we're all over the place, and we're not coming up with anything. >> since dirt and grass stains were found on devon's pants, investigators decided to spray items in the couple's backyard with fluorescein. there on a pool cover and on