Blood Secrets: Chronicles of a Crime Scene Reconstructionist (17 page)

If you tilt the surface the blood lands on, the droplets will start to develop a point. Picture a red teardrop with one rounded end and one pointed end, known in forensics as a “spine” or “tail.” What does this mean to a homicide detective or a crime scene reconstructionist in practical terms? Teardrop-shaped blood spatter tells you that blood hit a wall, floor, or Whatever other surface it landed on at an angle other than ninety degrees.

If you were to walk into a room where someone had been bludgeoned standing in front of a wall, you would probably see a bunch of blood droplets of various sizes, all with little tails pointed in the same direction. To reconstruct the crime, you would examine the stains to determine what direction the blood was traveling when it hit the wall, then measure the length and width of the bloodstains to pinpoint the
angle of impact
—the angle at which the blood hit the wall—using the ground as your baseline. You could tape a long string through each droplet until you found the point where all those strings intersected, and that would give you the approximate spot where blood hit the wall first—the
point of convergence
or
point of origin
, in forensic lingo. Now you can also take a digital photograph of the blood spatter, upload it to a computer, and use specialized software to calculate the angle.

Angular drops

The more elongated the blood droplets on the wall, the more extreme the angle of impact. What causes an extreme angle? Standing closer to the wall. If you’re scrutinizing blood spatter and you calculate the angle of impact at fifteen degrees (again, using the floor as your baseline), you’ll know that the victim had his face practically pressed up against the blood-spattered surface when he was murdered.

To reconstruct the crime, you would also photograph and possibly videotape the crime scene from every angle possible and write down every measurement you took to make sure you didn’t distort the scale of the bloodstains. Then you would combine the data you collected
with other evidence like the victim’s wounds to get an accurate mental picture of what happened. Where was the victim when he was attacked? Was he standing? Kneeling? Lying on the floor? Was he facing his attacker or hit from behind? Was the body moved after death? Does the blood evidence belie or support the suspect’s claim that he killed his victim in self-defense? Remember, the truth can exonerate as well as implicate.

Admittedly, there are some limits to reading the shapes in blood spatter. For instance, the smaller the drop, the harder it is to discern directionality. The weave of certain types of clothing and fabrics can influence a blood droplet’s shape, too, and mislead a crime scene analyst.

But in the right circumstances, understanding the
directionality
of blood drops can help you determine which way a killer leaving a scene headed and how fast he moved. You would use what the blood trail told you to reconstruct the crime more accurately or, if you were extremely lucky, to follow and catch an escaping killer.

Say you’re a cop responding to a 911 call made by a civilian claiming she heard shouts, screaming, and the sounds of fighting in the apartment next to hers. You arrive at the crime scene to find a bleeding, unconscious man who has obviously been in a knife fight. A trail of blood droplets leads out the back door and down a stairwell. You would use what you know about blood patterns to determine whether the attacker walked or ran, how long ago he left (blood starts to dry in three to six minutes), and whether he was bleeding or got his victim’s blood on himself—all of which would give you and your fellow officers solid information about what to look for in suspects in the immediate vicinity.

One simple strategy I often recommend to jurors to help them visualize concepts like satellite spatter and teardrop-shaped droplets is to experiment with water. Drip water into a puddle and you’ll see the
droplets rebound to the sides. Flick water from your fingertips at a fogged-up shower door from various angles and you’ll notice that the droplets’ tails change as you shift your position.

If you strike a source of wet blood with a moderate amount of force, you’ll produce
medium-velocity blood spatter
. The majority of homicides where you find it involve blunt-trauma attacks such as beatings and bludgeonings or stabbings. But since anything with greater force than gravity but weaker force than a gunshot will generate medium-velocity blood spatter, the possibilities are endless. Remember the old game of Clue? Aside from the rope and the revolver, all of the hypothetical weapons would produce medium-velocity spatter—the wrench, the lead pipe, the candlestick, or the knife. The force applied to the blood source (usually the victim’s body) means the blood travels faster and produces smaller airborne droplets than it would in a low-velocity pattern. The increased impact of the blood droplets when they land produces a random smattering of large and small drops. They are easier to see with the naked eye than high-velocity spatter, which usually requires magnification.

Medium-velocity blood spatter

Here’s a key concept in many criminal cases that tends to surprise jurors and lawyers: It requires multiple blows to a victim’s body to produce medium-velocity spatter. Say a robber caught in the act hits a gas station attendant over the head with a tire iron and crushes his skull. The first blow would expose the victim’s blood but would not send any of it flying onto his surroundings. It’s the subsequent blows that would create blood spatter on the walls, ceiling, and nearby objects like the cash register.
The first blow creates no blood spatter
. If there were five blows to the station attendant’s head, you will find spatter from four. You won’t be able to count the blows by examining the spatter, though, unless victim and attacker moved significantly after each one.

If the hypothetical tire iron murder did involve multiple blows, forensic examination would probably also reveal bits of tissue, bone, and brain matter embedded in the spatter. Detectives could use the stains to calculate the flight path of the blood and the angle of impact and look for voids in the blood spatter to give them an indication of where the murderer and any accomplices were standing when the subject was beaten to death.

Generally speaking, the blunter the weapon, the more blood spatter results. Bigger weapons produce more spatter because a larger surface area is striking the blood, and sharp objects like knives create less spatter than rocks or sledgehammers unless they slice open an artery. When that happens, you get an arterial spurt, where the heart forcefully pumps blood out of the body through the wound, creating a series of
long, arced lines of medium-velocity spatter. We call this type of stain a
projected blood pattern
rather than an impact pattern because it’s created by blood released under pressure—not by an object striking liquid blood. The bloody puddles junkies leave behind when they jettison their blood after it gets drawn back into a syringe during a fix are also considered projected blood.

Other factors influence the amount of blood spatter, too. What part of the body did the murderer strike? Was the victim wearing heavy clothes? Was he wearing a hat?

As I mentioned in the previous chapter, another concept people find hard to grasp is that assailants often get very little blood on themselves during a beating or stabbing, even if it’s an extremely bloody one. That’s because in most blunt-trauma attacks, the majority of the blood is directed outward. The blood that lands on the person wielding the weapon is often minimal. You have to examine a killer’s clothing under high-intensity lights or apply a blood reagent to it to spot the telltale traces of medium-velocity blood spatter.

If you can read blood evidence well enough to understand what it suggests about the victim’s position and the assailant’s MO, you’ll get an idea of where to look for small deposits of blood spatter on the killer’s clothes. Did the victim suffer overhead blows while lying on the ground? The assailant likely got some amount of spatter on the bottom of his pants, socks, and shoes. Did the killer use wide swings to the side like a batter playing baseball? Odds are spatter landed on his sleeves, hands, or gloves during the attack. Did he swing right-or left-handed? The spatter patterns on his sleeves, pants, and shoes will probably reflect that.

If the murder is premeditated and the killer wore protective clothing during the attack, minute traces of medium-velocity spatter can still show up in unlikely spots he’s overlooked. I’ve investigated cases where there wasn’t a trace of blood on a suspect’s clothes, but minuscule flecks of blood on his glasses, his watch, or his belt buckle gave him away.

Cast-off

One other blood pattern that commonly accompanies medium-velocity spatter is
cast-off
—blood that flies off an object while it’s in motion. It could result from a person with bloody hair whipping his head around. Or someone with blood-soaked sleeves swinging his arms as he runs could produce it. But usually at crime scenes, it gets inadvertently flung off a weapon being used to make multiple blows. (Think of Lizzie Borden and the infamous “forty whacks” with the ax, for example, though in reality it was fewer than twenty.)

Cast-off can land on items at the crime scene or on a killer’s clothing. If two suspects admit to being present at a murder, but each claims he stood by and watched while the other committed it, cast-off blood patterns sometimes provide the only definitive proof as to who actually wielded the murder weapon. (Incidentally, if blood pattern analysis
had been well developed in 1892, experts might have been able to determine whether Borden was likely guilty or innocent based on cast-off and impact spatter patterns at the scene, on her clothing, and on the hatchet believed to be the murder weapon.)

Medium-velocity spatter figured heavily into the case of prominent Massachusetts allergist Dirk Greineder. On the morning of October 31, 1999, sixty-year-old Greineder and his wife of thirty-one years—Mabel, or May, as her friends called her—took their German shepherd for a walk in the woods surrounding Morses Pond near their home in Wellesley. With their three children grown and living on their own, the couple often walked their dogs together for exercise. But according to the story Greineder later told police, May suffered frequent back pain, and when it flared up that day, she decided to go back to the van to wait while he continued walking Zephyr.

When Greineder was returning to the vehicle a short time later, he stumbled upon his wife sprawled across a wooded trail. At first he thought she was resting her back, but bending closer, he discovered to his horror that her throat had been slashed and she had been hit in the head multiple times with what police learned was a blue-handled hammer when they found the weapon along with a pocketknife and a bloodstained glove under the grate covering a nearby storm drain. Further searching turned up a matching bloody glove under a second grate.

Greineder’s version of events began to fall apart when lab tests confirmed not only that the bloodstains were May’s, but that the pocket-knife and one of the gloves bore traces of her husband’s DNA. A police sergeant securing the crime scene noted that though the man’s Wind-breaker, shoes, and glasses were bloody, his hands were spotless—surprising,
considering he claimed to have tried twice to lift May’s body and to have checked her carotid artery for a pulse. A trash bag, surgical gloves, and lighter fluid with a label advertising its stain-removing abilities found under a pile of leaves nearby pointed to premeditated murder. When a pair of brown work gloves identical to the bloody ones were retrieved by police from a dog house at the Greineders’ home, suspicion mounted.