>> in murder cases constructed on the interpretation of blood evidence, it's not unusual for juries to hear from dueling experts when they go to trial, and that's what happened here. it was seen as a coup for the defense that it locked up one of the most highly regarded blood spatter experts in the nation, tom bevel, a veteran of almost three decades with the oklahoma city pd. he'd even mentored the blood expert used by the prosecution. >> i was hired either the next day or within two days at least of the actual crime by the defense. >> and they thought they were very clever because they took you, in effect, off the market. the prosecution wouldn't be able to tap your expertise. >> i believe they would have thought that, yes. >> as expected his take put his client, dr. hamilton,a better light. for instance, the shirt the prosecution suggested had a blood stain left by the murder weapon, the defense's expert, bevel, couldn't go that far. >> in order to say that, you have to have the murder weapon.