When the detectives arrived at the Eighth Street address there was no yellow tape ringing the property, no sector cars blocking traffic, none of the blue and white Crime Scene Unit vans, no officer guarding the entrance, crime-scene log in hand. All this was long gone.

They had read the reports, seen the autopsy protocol, viewed the photographs and video. But they had not yet followed the path of the killer.

Both detectives believed that their investigation would truly begin the moment they stepped into the room where Caitlin O’Riordan had been found.

THE BUILDING HAD BEEN SEALED four months earlier at the time of the initial investigation, the doors replaced and padlocked, the plywood over the windows secured with lag bolts. Originally a single-family row house, this corner building had been bought and sold many times. Its most recent incarnation was as a small grocery, a narrow, slipshod emporium hawking baby formula, chips, diapers, canned meats, magazines, lottery dreams. Its stock-in-trade, its lifeblood, had been the Holy Trinity of crack addiction: Chore Boy scouring pads, disposable plastic lighters, and individually packaged tea roses. The roses came in long, narrow glass tubes which, within a minute or two of leaving the store, became straight shooters, a fast and easy way to fire up a rock, the ashes from which were caught by the steel wool of the scouring pad. Every convenience store in the Badlands carried tea roses, which probably made this part of North Philly the most romantic place on earth. Hundreds of times a day someone bought a flower.

The bodega had closed more than three years earlier, and no tenant had moved in. The building’s façade was still a Day-Glo green, with a strange sign painted over the front window:

OPEN 24 HOURS.

DAYS 12 TO 8 PM.

Jessica unlocked the padlock on the corrugated metal door, rolled it up. They stepped inside and were immediately greeted with the unpleasant odor of mold and mildew, the chalky scent of damp plaster. It was late August and the temperature outside was eighty-eight degrees. Inside it had to be nearing a hundred.

The first floor was remarkably clean and tidy, except for a thick layer of dust on everything. Most of the trash had long ago been collected as evidence and removed.

To their left was what was once the counter; behind it, a long row of empty shelves. Above the shelves lingered a few remaining signs—KOOLS, BUDWEISER, SKOAL—along with a menu board offering a half dozen Chinese takeout items.

The stairwell down was at the back of the building on the left. As Jessica and Kevin began to descend the steps they clicked on their Maglites. There was no electricity here, no gas or water, no utilities of any kind. Whatever thin sunlight seeped through the cracks between the sheets of plywood over the windows was instantly swallowed by the darkness.

The room where Caitlin O’Riordan was found was at the basement’s far end. Years ago, the small windows at street level had been bricked in. The gloom was absolute.

In the corner of the room was a glass display case, a commercial beverage cooler used at one time for beer and soda and milk. It had stainless steel sides, and stood more than six feet tall. It was in this glass coffin that Caitlin’s body had been discovered—sitting on a wooden chair, staring out at the room, eyes wide open. She’d been found by a pair of teenage boys scrapping for copper.

Byrne took out a yellow legal pad and a fine point marker. Holding his flashlight under his arm, he made a detailed sketch of the subterranean room. In homicide work, the investigating detectives were required to make a diagram of every crime scene. Even though photographs and videotape records of the scene were made, it was the investigator’s sketch that was most often referred to, even in the trial stage. Byrne usually made the diagram. By her own admission, Jessica couldn’t draw a circle with a compass.

“I’ll be upstairs if you need me,” Jessica said.

Byrne glanced up, the darkness of the room a black shroud around his broad shoulders. “Gee thanks, partner.”

JESSICA SPREAD OUT THE FILES on the front counter, grateful for the bright sunlight streaming through the open door, grateful for the slight breeze.

The first page of the binder was a large photograph of Caitlin, a color eight-by-ten. Every time Jessica looked at the photograph she was reminded of the Gene Hackman movie Hoosiers, although she would be hard-pressed to explain why. Perhaps it was because the girl in the picture was from rural Pennsylvania. Perhaps it was because there was an openness to the girl’s face, a trusting countenance that seemed locked into the world of 1950s America—long before Caitlin’s birth, life, and death—a time when girls wore saddle shoes and kneesocks and vest sweaters and shirts with Peter Pan collars.

Girls didn’t look like this anymore, Jessica thought. Did they?

Not in this time of MySpace and Abercrombie & Fitch catalogs and rainbow parties. Not in this day and age when a girl could buy a bag of Doritos and a Coke, board a bus in Lancaster County, and ninety minutes later emerge in a city that would swallow her whole; a trusting soul who never had a chance.

The estimated time of Caitlin’s death was between midnight and 7 AM on May 2, although the medical examiner could not be more precise, given that by the time Caitlin O’Riordan’s body had been discovered she had been dead at least forty-eight hours. There were no external wounds on the victim, no lacerations or abrasions, no ligature marks to indicate she may have been restrained, no defensive wounds that would suggest she struggled with an assailant. There had been no skin or any other kind of organic matter beneath her fingernails.

At the time she was discovered, Caitlin had been fully clothed, dressed in frayed blue jeans, Reeboks, black denim jacket, and a white T-shirt. She also wore a lilac nylon backpack. Around her neck had been a sterling silver Claddagh, and although it was not particularly valuable, the fact that she wore it in death did not support any theory that she had been the victim of a robbery gone bad. Nor did the cause of the death.

Caitlin O’Riordan had drowned.

Homicide victims in North Philadelphia were generally not drowned. Shot, stabbed, bludgeoned, sliced and diced with a machete, pummeled with an ax handle, yes. Popped by a rebar, run over with a Hummer, stuck with an ice pick, doused with gasoline and lit ablaze—yeah, all the time. Jessica had once investigated a North Philly homicide committed with a lawn edger. A rusty lawn edger.

But drowned? Even if the vic was found floating in the Delaware River, the cause of death was usually one of the above.

Jessica looked at the lab report. The water in Caitlin’s lungs had been carefully analyzed. It contained fluoride, chlorine, zinc orthophosphate, ammonia. It also contained trace levels of haloacetic acid. The report contained two pages of graphs and charts. It all went way over Jessica’s head, but she had no problem at all understanding the report’s conclusion. According to the forensics lab and the medical examiner’s office, Caitlin O’Riordan did not drown in the Delaware or Schuylkill River. She did not drown in Wissahickon Creek, nor in any of the fountains for which the City of Brotherly Love was rightly known. She did not drown in a swimming pool, public or private.

Caitlin drowned in ordinary Philadelphia tap water.

The original investigators had contacted the Philadelphia Water Department and were told that, according to the EPA, the water found in Caitlin’s lungs was indeed specific to Philadelphia. The three treatment plants at Baxter, Belmont, and Queen Lane had all made specific adjustments to their drinking water processes in March, due to an oil-tanker spill.