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.