"The investigators working the Cherokee case are convinced it's a biker hit." I hesitated, unsure how to put my reservations into words. "I can't nail it down, but something about the scene struck me as being off."

"Off?"

I explained my assignment with Operation Carcajou, and what I'd seen at the briefing session.

"I realize I'm a novice, but maybe that's it. Maybe I'm seeing things through different eyes."

"And what do your eyes tel you?"

"That the Cherokee murder was sloppy."

"Anything else?"

"That the victim was sloppy. Apparently Cherokee admitted his kil er. Does that sound like a former member freelancing drugs on gang turf?"

I didn't mention Dorsey, or his claims of innocence. I figured the less said about my prison visit the better.

Gilbert looked at me a long time, then smiled.

"Claudel thinks you're an interfering pain in the ass.

"I think highly of him, as wel ."

He threw back his head and laughed, then his face grew serious.

"How much do you know about blood-spatter analysis?"

"Not much," I admitted.

"Ready for a crash course?"

I nodded.

"O.K. Here goes."

He leaned back and raised his eyes to the ceiling, no doubt deciding where to begin and how to condense years of training into a brief lecture. I could picture him doing the same for a jury.

"A free-fal ing drop of blood is spherical due to the effects of gravity and surface tension. Think about when you prick your finger. Blood builds up on the down side until the drop is able to break free and fal . Seems simple, right?"

"Yes."

"It's not. Al kinds of opposing forces are at work. Gravity and the increasing weight of the blood are 'pul ing' the drop downward. At the same time the surface tension of the blood is trying to reduce the exposed surface of the drop and is 'pushing' it upward."

He gestured quotation signs around the verbs.

"Only when the 'pul ing' forces exceed the 'pushing' forces wil the drop break free. Initial y it's elongated, but as it fal s the drop flattens due to air resistance. The attractive forces of surface tension within the drop cause it to assume a shape with the least amount of surface area. Thus, drops of blood are shaped like spheres, not like teardrops as they're usual y drawn. And shape is one of the things we consider in spatter-pattern analysis.

"A blood spatter is produced as a result of a force striking static blood. It could be in a pool on the sidewalk, or inside a victim s head. When hit, the blood breaks into drops, cal ed spatter, which travel through the air as spheres."

I nodded.

"When these spheres strike a surface they leave predictable types of trails. Bloodstain-pattern interpretation is concerned with examining stains produced by drops of blood that are not typical. The stains and trails have been altered in some way, usual y by violent activity.