The flat roofs across the street were checkered with black shadows. In the dim yellow light of a city sky at night, Sgt. Lorenzo Martinez thought he saw a man move.

He jumped away from the window and pressed his back to the wall.

Maybe, he thought, he was becoming too cautious, too wary. Ever since six of his friends in Alpha Company had been killed in hidden-bomb attacks in Iraq, he had been easily spooked.

His mind raced. Was the door locked? Was there a route of escape? What would he do without a weapon?

With just thumb and forefinger, he slowly separated the blinds and peered out again.

He froze.

Sure enough, it was a sniper.

But this was Philadelphia, not Baghdad, and Martinez was in his own bedroom on the second floor of his own house on North Fifth Street.

Somehow, the bald, 44-year-old father of two had transported himself back to Iraq, back to the dusty roads and drab villages where the bomb attacks that his outfit suffered in 2004 and 2005 made it the hardest-hit Pennsylvania National Guard unit since World War II.

This evening in June 2006, he'd had a couple of beers. He and his wife, Maria, had exchanged sharp words. His eyes, flashing in the round mirror on the dresser, had grown wild.

Now he yanked open the drawers and dumped them on the floor. He turned over the mattress and shoved it, with other furniture, against the door.

With the lights out, he stood staring at imagined danger across the way.

He began to dwell on the faces of the men who'd been lost - members of the First Battalion of the 111th Infantry, based at an armory in Northeast Philadelphia.

There was Spec. Gennaro Pellegrini, a police officer who boxed professionally and was known as "Punchy." Martinez could picture him all worked up, ready for a fight.

There was Sgt. Brahim Jeffcoat, long-faced and lean, who was a Temple University student and father of a 19-month-old girl. His round glasses gave him a studious look.

There was Nathaniel DeTample, a former 130-pound wrestler at Pennsbury High School in Bucks County. At 19, he was a rarity in Alpha: a private first class in the veteran unit. Martinez always thought he looked like a baby.

Martinez could bring to mind all the faces - of those three and of the others, Spec. Kurt Krout, Sgt. Francis Straub, Spec. John Kulick. They had been killed in a pair of bomb blasts three days apart in August 2005. The calamity had been major news across the state.

During his night of distress, Martinez had these men on his mind. "Where," he wanted to know, "are my friends?"