We moved to the far wal , where he indicated an area that looked as if it had been spray-painted.

"High-velocity-impact spattering means a force velocity greater than one hundred feet per second and results from gunshots, explosions, and mechanical accidents. It's more like a mist, with individual spatters averaging less than one mil imeter in diameter.

"But don't get me wrong. Not every spatter fal s neatly into one of these categories. Blood that is splashed, cast off, or projected can real y complicate a picture."

"How so?"

"These are actual y forms of low- to medium-velocity spatter, but they differ from the ones I just described. For example, splashed blood results from someone stepping into already-pooled blood. This leaves long, narrow spatters surrounding a central stain, with very few round stains present.

"Projected blood results from someone running through, stamping into, or slapping a pool of blood. Or from arterial gushing, or beating a head on the floor Again there are long, spiny spatters radiating from a central stain. But in this case the borders of the central stain are also distorted.

"Blood cast off from a weapon leaves yet another pattern. Let me show you.

He went back to the rod, dipped, and swung it in an arc. Blood flew from the tip and struck the wal to his right. I drew close and studied the stain.

"Cast-off drops are smal er than those in typical low-velocity spatter, and the greater the force the smal er the drops. Also, since the blood is being thrown from a moving object, cast-off spatter occurs in straight or slightly curved trails, and the drops are fairly uniform throughout."

"So you can determine the nature of an assault based on the size and shape of the spatter?"

"Yes, And in most cases we can pinpoint where the attack took place. Let's go back to my office and I'l show you something else."

When we were once again in front of the computer he placed his hands on the keyboard and entered a command.

"You saw us taking videos of the bloodstains in the victim's apartment, right?"

"Yes."

"We used a simple video camera, but you can also use digital. We recorded each area of spatter using a scale and a plumb line."

"Why a plumb line?"

"The program uses that to determine the vertical direction of the stain.

Gilbert hit a key and a cluster of el iptical brown forms came up on the monitor

"The images on the videotape are entered into the computer and can be played back on the monitor Single frames are grabbed and recorded on the hard disk as bitmaps. A program then displays the image of each stain so we can take measurements. The measurements are used to calculate two angles: the angle of directionality and the angle of impact."

More keystrokes, and an oval-shaped white outline appeared superimposed over the stain at center screen. Gilbert pointed at it.