THE PRESENCE OF BLOOD AT A CRIME SCENE IS ALWAYS OF IMPORTANCE, BUT THE QUESTION IS USUALLY ONE OF DETERMINING FROM WHOM THE BLOOD CAME. BLOOD EVIDENCE, HOWEVER, CAN ALSO BE USED TO ASCERTAIN AND RECONSTRUCT THE FACTUAL CIRCUMSTANCES WHICH EXISTED AT THE TIME OF THE EVENT. AN EXAMPLE IS PRESENTED IN WHICH BLOOD EVIDENCE PROVIDED DEFINITIVE PROOF OF THE POSITION OF CERTAIN WEAPONS AT THE SCENE. A SUSPECT ADMITTED HAVING SHOT THE VICTIM, BUT CLAIMED THAT THE SHOOTING WAS COMMITTED IN SELF-DEFENSE WHEN THE VICTIM ATTACKED HIM WITH A HATCHET AND A CLEAVER. THESE TWO WEAPONS, FOUND ON THE TOP OF A DRESSER, WERE SPATTERED WITH THE 'FOG' OF BLOOD CREATED BY THE EXPLOSIVE IMPACT OF THE BULLET ENTERING OR EXITING THE VICTIM'S BODY. A LUMINOL TEST, WHICH INVOLVES SPRAYING THE AREA WITH THE LUMINOL REAGENT IN COMPLETE DARKNESS, WAS CONDUCTED; PHOTOGRAPHS OF THE LIGHT-EMITTING CHEMICAL REACTION BETWEEN THE LUMINOL AND THE BLOOD SHOWED THAT THE AREA BENEATH THE HATCHET AND CLEAVER WAS DEVOID OF BLOOD DROPLETS, INDICATING THAT THE WEAPONS HAD NOT FALLEN TO THE DRESSER TOP AS THE VICTIM WAS STRUCK, BUT HAD BEEN PLACED THERE EARLIER. METALS FOR WHICH LUMINOL IS NOT A SPECIFIC REAGENT, RESULTING IN FALSE POSITIVE OR NEGATIVE REACTIONS, ARE LISTED. DETAILED INSTRUCTIONS FOR ADMINISTERING A LUMINOL TEST, ALONG WITH CAMERA AND FILM INFORMATION FOR PHOTOGRAPHING THE REACTION, ARE ALSO PRESENTED. (DAS)