In last month's forensic column I described a scene where two officers responding to crime scene find several victims apparently murdered in a private home. One officer has entered at the front of the house and has found three victims, two in the living room and another in a hallway. All victims has apparently been shot and beaten with some blunt object. The second officer entered at the rear of the home has found another victim in the kitchen.
As the first officer makes his way down the hallway to the kitchen, he must pass by the victim on the floor. There is blood spatter everywhere on the walls and ceiling. From the swipe pattern on the floor, it is obvious that the victim was severely beaten and had crawled along the floor, possibly attempting to evade her attacker. The hallway is narrow, and in order to get past the victim without stepping in any of the blood, the officer reaches out to put his hand against the wall to steady himself. It is at that point that some critical bloodstain evidence may be lost.
Bloodstain Patterns Tell a Story
Blood spatter patterns on walls and ceiling can provide a wealth of information about both the events that occurred and about the attacker. The angle at which blood droplets hit the wall can tell where the victim and attacker were at the time the spatter was made. The degree to which the droplets are elongated or teardrop-shaped can be used to determine the velocity that the blood was traveling at the time of impact and the relative ferocity of the blow dealt to the victim. The direction that blood is cast off relative to the victim can determine whether the attacker is right or left handed, clearly a vital piece of information. It is also possible, in some cases, to determine that a second attacker was involved in an event, even when no other information indicates their presence.
Bloody finger- or palm prints are often left on walls, doors, and door jams by perpetrators in their haste to leave the scene. All of this information can be compromised in a moment by an officer's careless action. A hand along a wall can smear vital blood patterns or a fingerprint. Even brushing against bloodstain evidence with your sleeve or coat can obscure vital evidence.
The Devil is in the Detail
That may be an old saying, but it could never be truer than in bloodstain analysis. Let's look at a hypothetical situation. A woman is beaten to death in her kitchen. The husband says he came home and found her body and called police. The husband claims that he knelt down to see if his wife was alive and to hold her. This explains the transfer blood pattern of her blood on his clothes. There is blood spatter on the wall and ceiling next to her body. He next claims that as he got up to call police, his foot slipped in the blood on the floor and he put his hand out on the wall to get his balance. In doing that, his hand made a swipe pattern through some of the blood spatter, and at the end of the swipe he left a clear print of his right thumb and index fingers. There is a clear swipe mark in the blood on the floor, consistent with the husband slipping in the blood, which also explains her blood on his shoes. There is also a swipe mark about two feet long thru the spatter pattern on the wall. At the end of the swipe is a set of bloody fingerprints. When the prints are lifted and analyzed, they are found to be that of the husband's right thumb and index fingers. All this is consistent with the husband's story of what happened after he arrived home and found his dead wife on the floor of their kitchen.
The CSI team photographs all the bloodstain evidence and makes all of their measurements of blood droplet trajectory angles, so a determination of where the body and attacker were at the time of the beating can be made. From this analysis, it is also determined that the perpetrator was left handed. The husband is right handed, an additional reason to clear the husband of suspicion. The CSI technicians, also as routine practice, cut out and remove several section of drywall from the hallway and an additional section from the ceiling where it abuts the wall. They are placed in the evidence bin and stored.
The husband's story seems solid, and so investigators begin searching for other suspects. They might have looked for a long time had it not been for a bloodstain analyst that the prosecutor's office brought in to look at the evidence. Upon examination of that section of wall where the husband's hand swipe was, he observed something strange, something that had been missed by the other investigators. The wall did not have two bloodstain patterns--it actually had three. Blood droplets spattered on the wall during the beating had been smeared by the hand and what are called "skeleton" stains were left. These stains have a ring of dried blood around the outside, but are clear in the center where the still-liquid blood had been wiped away. This was certainly consistent with the husband's story of why his fingerprints are on the wall. However, it does mean that the husband was there not too long after the attack took place, because the blood droplets were not totally dried.
The Missing Piece
Then the investigator startled everyone by announcing that the husband was there during the beating. On the surface of the swipe pattern was additional blood spatter, and these droplets were intact, not skeletons. The only conclusion was that they had occurred after the hand swipe was made, and that means that the husband was present before the end of the beating. But the attacker was left-handed and the husband right-handed. While this new evidence did not make him the attacker, per se, it did place him there at the time of the crime.
Renewed investigation revealed that the husband and a male co-worker were having an affair, and that they had conspired to kill the wife. Both were eventually arrested and convicted of the murder of the wife. If this blood evidence had not been accurately detected, the husband and his accomplice might have gotten away with murder.