'Hey, Freddie, get up.' A flashlight shone on his face.

He raised a bandaged hand to his eyes, squinting as small suns probed the darkness of his tunnel.

'Come on, get up. What'd you do to your hand?'

'Frostbite,' he mumbled, staggering to his feet.

'You got to take care of yourself. You know you can't stay here. We got to walk you out. You want to go to a shelter?'

'No, man.'

'Freddie,' the officer went on in a loud voice, 'you know what's happened down here? You heard about Officer Davila?'

'I dunno nothing,' Freddie swayed and caught himself, squinting in the lights.

'I know you know Davila. You call him Jimbo.'

'Yeah, Jimbo. He's all right.'

'No, I'm afraid he's not all right, Freddie. He got shot down here tonight. Someone shot Jimbo and he's dead.'

Freddie's yellow eyes got wide. 'Oh no, man.' He cast about as if the killer might be looking on - as if someone might want to blame him for this.

'Freddie, you seen anybody down here tonight you didn't know? You seen anybody down here who might have done something like that?'

'No, I ain't seen nothing.' Freddie almost lost his balance and steadied himself against a concrete support. 'Not nobody or nothing, I swear.'

Another train burst out of the darkness and blew past on southbound tracks. Freddie was led away and we moved on, sidestepping rails and rodents moiling beneath trash. Thank God I had worn boots. We walked for at least ten minutes more, my face perspiring beneath my mask as I got increasingly disoriented. I could not tell if round bright lights far down the tracks were police flashlights or oncoming trains.

'Okay, we've got to step over the third rail,' Commander Penn said, and she had stayed close to me.

'How much farther?' I asked.

'Just down there, where those lights are. We're going to step over now. Do it sideways, slowly, one foot at a time, and don't touch.'

'Not unless you want the shock of your life,' an officer said.

'Yeah, six hundred volts that won't let go,' said another in the same hard tone.

We followed rails deeper into the tunnel as the ceiling got lower. Some men had to duck as we passed through an arch. On the other side, crime scene technicians were scouring the area while a medical examiner in hood and gloves examined the body. Lights had been set up, and needles, vials, and blood glistened harshly in them.

Officer Davila was on his back, his winter jacket unzipped, revealing the stiff shape of a bulletproof vest beneath a navy blue commando sweater. He had been shot between the eyes with the.38 revolver on top of his chest.

'Is this exactly as he was found?' I asked, stepping close.

'Exactly as we found him,' said a detective with NYPD.

'His jacket was unzipped and the revolver was just like that?'

'Just like that.' The detective's face was flushed and sweating, and he would not meet my eyes.

The medical examiner looked up. I could not make out the face behind the plastic hood. 'We can't rule out suicide here,' she said.

I leaned closer and directed my light at the dead man's face. His eyes were open, head turned a little to the right. Blood pooled beneath him was bright red and getting thick. He was short, with the muscular neck and lean face of someone who was seriously fit. My light traveled to his hands, which were bare, and I squatted to take a closer look.

'I see no gunshot residue,' I said.

'You don't always,' said the medical examiner.

'The wound to his forehead is not contact and looks to me as if it's slightly angled.'

'I would expect it to be slightly angled if he shot himself,' the medical examiner replied.

'It's angled down. I wouldn't expect that,' I said. 'And how did his gun come to rest so neatly on his chest?'

'One of the street people in here might have moved it.'

I was beginning to get annoyed. 'Why?'

'Maybe someone picked it up and then had second thoughts about keeping it. So he put it where it is.'

'We really should bag his hands,' I said.

'One thing at a time.'

'He didn't wear gloves?' I squinted up in the circle of bright light. 'It's very cold down here.'

'We haven't finished going through his pockets, ma'am,' said the woman medical examiner, who was the young, rigid sort I associated with anal-retentive autopsies that took half a day.

'What is your name?' I asked her.

'I'm Dr. Jonas. And I'm going to have to ask you to back away, ma'am. We're trying to preserve a crime scene here and it's best you don't touch or disturb anything in any way.' She held up a thermometer.

'Dr. Jonas' - and it was Commander Penn who spoke - 'this is Dr. Kay Scarpetta, the chief medical examiner of Virginia and consulting forensic pathologist for the FBI. She is quite familiar with preserving crime scenes.'

Dr. Jonas looked up and I caught a glint of surprise behind her face shield. I detected embarrassment in the long moment it required her to read the chemical thermometer.

I leaned closer to the body, paying attention to the left side of his head.

'His left ear is lacerated,' I said.

'That probably happened when he fell,' said Dr. Jonas.

I scanned the surroundings. We were on a smooth concrete platform. There were no rails to strike. I shone my light over concrete supports and walls, scanning for blood on any structure that Davila might have hit.

Squatting near the body, I looked more closely at his injured ear and a reddish area below it. I began to see the class characteristics of a tread pattern that was wavy with small holes. Under his ear was the curve from the edge of a heel. I stood, sweat rolling down my face. Everyone was watching me as I stared down the dark corridor at a light getting closer.

'He was kicked in the side of the head,' I said.

'You don't know that he didn't hit his head,' Dr. Jonas said defensively.

I stared at her. 'I do know,' I asserted.

'How do we know he wasn't stomped?' an officer asked.

'His injuries are inconsistent with that,' I replied. 'People usually stomp more than once and in other areas of the body. I would also expect there to be injury to the other side of his face, which would have been against the concrete when the stomping occurred.'

A train blew by in a rush of warm, screeching air. Lights floated in the distant dark, the figures attached to them shadows with voices that faintly carried.

'He was disabled by a kick, then shot with his own gun,' I said.

'We need to get him to the morgue,' the medical examiner said.

Commander Penn's eyes were wide, her face upset and angry.

'It's him, isn't it?' she said to me as we began to walk.

'He's kicked people before,' I said.

'But why? He has a gun, a Clock. Why didn't he use his own gun?'

'The worst thing that can happen to a cop is to be shot with his own gun,' I said.

'So Gault would have done that deliberately because of how it would make the police… make us feel?'

'He would have thought it was funny,' I said.

We walked back over rails and through trash alive with rats. I sensed Commander Penn was crying. Minutes passed.

She said, 'Davila was a good officer. He was so helpful, never complained, and his smile. He brightened a room.' Her voice was clenched in fury now. 'He was just a goddam kid.'

Her officers were around us but not too close, and as I looked down the tunnel and across the tracks, I thought of the subterranean acres of twists and turns of the subway system. The homeless had no flashlights, and I did not understand how they could see. We passed another squalid camp where a white man who looked vaguely familiar sat up smoking crack from a piece of car antenna as if there were no such thing as law and order in the land. When I noticed his baseball cap the meaning didn't register at first. Then I stared.

'Benny, Benny, Benny. Shame on you,' one of the officers impatiently said. 'Come on. You know you can't do this, man. How many times are we going to go through this, man?'

Benny had chased me into the medical examiner's office yesterday morning. I recognized his filthy army pants, cowboy boots and blue jean jacket.

'Then just go on and lock me up,' he said, lighting his rock again.

'Oh yeah, your ass is gonna be locked up, all right. I've had it with you.'

I quietly said to Commander Penn, 'His cap.'

It was a dark blue or black Atlanta Braves cap.

'Hold on,' she told her troops. She asked Benny, 'Where did you get your cap?'

'I don't know nothing,' he said, snatching it off a tuft of dirty gray hair. His nose looked as if something had chewed on it.

'Of course you do know,' the commander said.

He stared crazily at her.

'Benny, where did you get your cap?' she asked again.

Two officers lifted him up and cuffed him. Beneath a blanket were paperback books, magazines, butane lighters, small Ziploc bags. There were several energy bars, packages of sugarless gum, a tin whistle and a box of saxophone reeds. I looked at Commander Penn, and she met my eyes.

'Gather up everything,' she told her troops.

'You can't take my place.' Benny struggled against his captors. 'You can't take my motherfucking place.' He stomped his feet. 'You goddam son of a bitch…'

'You're just making this harder, Benny.' They tightened his cuffs, a cop on each arm.

'Don't touch anything without gloves,' Commander Penn ordered.

'Don't worry.'

They put Benny's worldly belongings in trash bags, which we carried out with their owner. I followed with my flashlight, the vast darkness a silent void that seemed to have eyes. Frequently, I turned back and saw nothing but a light I thought was a train, until it suddenly moved sideways. Then it became a flashlight illuminating a concrete arch Temple Gault was passing through. He was a sharp silhouette in a long dark coat, his face a white flash. I grabbed the commander's sleeve and screamed.