With only a few available on each shift to process evidence, the lab techs themselves are a limited resource. The tech working your scene may have been pulled off a commercial robbery to work this homicide or may be needed a half hour later to work another shooting on the opposite side of town. And your own time is equally precious. On a jumping midnight shift, the hours you could spend at one scene might be divided between two homicides and a police shooting. And even with a single murder, hours spent at a scene have to be measured against time that could be spent interviewing witnesses who are waiting downtown.

Every scene is different, and the same detective who requires twenty minutes at a street shooting may spend twelve hours to process a double stabbing inside a two-story rowhouse. A sense of balance is required at both scenes, an understanding of what has to be done and what can reasonably be done to produce evidence. Also required is the persistence to oversee the essentials, to make sure that what’s being done is done correctly. On every shift, there are those lab techs who arrive at complex crime scenes and provoke sighs of relief from detectives, just as there are others who can’t lift a usable print if a suspect’s hand is attached to it. And if you want the photos to show the location of critical pieces of evidence, you better say as much, or the five-by-eight glossies will come back with every angle but the one you need.

These are the basic requirements. But there is something else about crime scenes, an intangible on the continuum between honed experience and pure instinct. An ordinary person, even an observant person, looks at a scene, takes in many of the details and manages a general assessment. A good detective looks at the same scene and comprehends the pieces as part of a greater whole. He somehow manages to isolate the important details, to see those items that conform to the scene, those that conflict, and those that are inexplicably absent. He who speaks of Zen and the Art of Death Investigation to a Baltimore homicide detective is handed a Miller Lite and told to stop talking communist hippie bullshit. But some of what happens at a crime scene, if not exactly antirational, is decidedly intuitive.

There is little else to explain Terry McLarney staring at the seminude body of an elderly woman, rigored in her bed with no apparent trauma, and deciding correctly-on the basis of an open window and a single stray pubic hair on the sheet-that he is working a rape-murder.

Or Donald Worden, walking down an empty East Baltimore street minutes after a fatal shooting, putting his hand on the hood of one parked car out of twenty and feeling the heat of an engine-a sure sign that the car was recently occupied by persons who fled rather than be identified as witnesses. “There was some condensation on the back window,” he says later, shrugging. “And it was a little ways from the curb, like the driver parked it in a hurry.”

Or Donald Steinhice, a veteran from Stanton’s shift, who is entirely convinced that the woman hanging from the ceiling of her bedroom has taken her own life, but somehow can’t leave the room until one last detail is settled in his mind. He sits there in the shadow of the dead woman for half an hour, staring at a pair of bedroom slippers on the floor below the body. The left slipper is below the right foot, the right below the left. Was she wearing the slippers on the wrong feet? Or did someone else, someone who staged the scene, place the slippers there?

“It was the only thing about that scene that really bothered me, and it bothered me for a good long while,” he later recalls, “until I thought about how a person takes off their bedroom slippers.”

Steinhice finally imagines the woman crossing her legs so as to wrap the toe of one slipper around the heel of the other, prying the slipper off from the back-a common maneuver that would leave the slippers on opposite sides.

“After that,” he says, “I could leave.”

In the clear sunlight of a winter morning, the academy trainees feel no sense of foreboding in the alley behind the rowhouses on Newington Avenue. As they crawl through its recesses and kick through its clutter, they find it to be an alley like any other.

Dressed in the khaki uniforms of the Education and Training Division, the class of thirty-two trainees begins the second day of the Latonya Wallace investigation by moving slowly through the alley and the back yards of every house in the block bounded by Newington and Whitelock, Park and Callow. They search inches at a time, stepping only where they have already searched, picking up each piece of trash with great care, then setting it down with the same deliberation.

“Go slowly. Check every inch of your yard,” Dave Brown tells the class. “If you find something-anything-don’t move it. Just go and grab a detective.”

“And don’t be afraid to ask questions,” adds Rich Garvey. “There’s no such thing as a stupid question. Or at least for right now, we’re going to pretend that there isn’t.”

Earlier, watching the trainees bound off a police department bus and count off for their instructor, Garvey expressed misgivings. Allowing a herd of new recruits to graze through a crime scene had all the makings of what detectives and military men like to call a clusterfuck. Visions of self-satisfied cadets trampling over blood trails and kicking tiny bits of evidence into sewer drains danced in Garvey’s head. On the other hand, he reasoned, a lot of ground can be covered with thirty-two interested persons, and at this point, the Latonya Wallace probe needs all the help it can get.

Once loosed upon the alley, the trainees are, to no one’s surprise, genuinely interested. Most of them attack the chore with zeal, picking through piles of garbage and dead leaves with all the fervor and devotion of the newly converted. It’s quite a sight, prompting Garvey to wonder what primal force of nature could inspire thirty patrol veterans to get down on their hands and knees in a Reservoir Hill alley.

The detectives divide the recruits into pairs and assign each to a rear yard behind the 700 block of Newington Avenue as well as the yards on Park and Callow avenues, which form the east and west boundaries of the block in which the child was found. There are no yards or open areas behind the block’s northern boundary, Whitelock Street; there, a red brick warehouse backs right up to the alley. The search takes more than an hour, with the trainees recovering three steak knives, one butter knife and one kitchen carving utensil-all marred by more rust than could accumulate on a murder weapon overnight. Also harvested are a variety of hypodermic syringes, an item commonly discarded by the local citizenry and of no particular interest to the detectives, as well as combs, hair braids, assorted pieces of clothing and a child’s dress shoe-none of it related to the crime. One enterprising recruit produces, from the rear yard of 704 Newington, a clear plastic bag half filled with a dull yellow liquid.

“Sir,” he asks, holding the bag up to eye level, “is this important?”

“That appears to be a bag of piss,” says Garvey. “You can put it down anytime you like.”

The search does not produce a child’s small star-shaped gold earring. Nor does it yield a blood trail, the one clue that might point to the murder scene, or at least the direction from which the body was carried to the rear of 718 Newington. Small purple blobs of coagulated blood dot the pavement where the little girl was discovered the morning before, but neither the detectives nor the trainees can locate another droplet anywhere else in the alley. The severity of the child’s wounds and the fact that she was carried to the alley wrapped in nothing more constricting than her little raincoat almost assures that the killer left blood spatters, but the rain that blanketed the city from late Wednesday to Thursday morning has neatly destroyed any such evidence.