It was an odd splash of color that jumped out from the drab gray shades of the dusty battleground in Iraq: a red shoe smaller than my hand, adorned with a pink ribbon and bow.

The sickening cacophony of war -- the crackle of gunfire, thud of artillery and bone-shaking tremors of air strikes -- drifted into a background haze.

I stood there staring at the shoe. The image remains so vivid in my mind I could paint it on a canvas from memory.

It was dusk on one of the first days of the November 2004 battle for Falluja. U.S. military commanders would later describe it as the most intense urban combat since Vietnam.

The shoe lay in a rubble-strewn yard amid the mustard yellow debris of a partially destroyed, single-story home in a poor part of the city.

My world froze right then.

I imagined her as being a little girl with curly, dark brown hair, about 5 years old. I could almost hear the shouts as she and other children ran around the yard playing joyfully.

There were other clues about the life of the family that once lived here. Torn photographs on the ground, a teddy bear in a drawer, clothing turned into clumps of matted shreds. A lone, delicate, hour-glass-shaped tea cup that somehow survived the American bombardment, peeking out from a heap of debris

Yet the inhabitants were gone, their stories untold, their lives a mystery.

Who was this little girl? Did she spend nights curled up in her parents' bed fearing the ghosts of al Qaeda operatives in the street? Did she burst into uncontrollable tears as the U.S. military pounded her city? Or did the family flee well before this all happened?

Was she even alive?

About a year later, I found myself at the exact same spot. I was on another embed -- one of dozens -- with the U.S. military. The house had been rebuilt; children darted through the yard.

I decided to knock on the door and ask about the little girl. I had a brief conversation with one of the men who answered. Like just about any Iraqi at the time, he was clearly uncomfortable with a Western TV crew and an entire platoon of American soldiers at his front door.

Falluja was no longer an al Qaeda stronghold, but its operatives still lurked in the shadows. Most of the city had been reduced to rubble.

The man told me the previous residents were distant relatives and had gone elsewhere. Realizing how distressed he and the other adults were, I thanked them and left. My desperate curiosity was trumped by the knowledge that our lingering presence could put them in danger if they were spotted talking to Americans.

And so that girl remains unknown to us, the outside world, like countless other Iraqi civilians caught in the middle of the invasion, the insurgency and the brutal sectarian violence that followed.

There were plenty of hair-raising moments in Falluja. We saw soldiers struck down; the festering corpses of insurgents rotting in the sun; the few remaining residents flocking to a mosque for food; the brave little boy, a bone protruding from his arm, who barely cried as the American medics tended to him.

And yet for me, Falluja is defined by that shoe, by the little girl whose story I don't know. One of many freeze-frame moments of human agony caused by war.

A month earlier, another battle zone was defined by another Iraqi I never met. The U.S. military had put word out to residents there to come and collect the bodies of the dead.

A woman clad in a black abaya, only her face visible, stumbled as she approached the hospital, arriving before the gates had even opened. It was as if each step was heavier than the last, as if her feet wanted to drag her away from what she knew she must see.

Then, she collapsed to her knees. Her black headdress fell off, her dark auburn hair tumbling out as she unleashed a scream filled with so much pain it felt like a claw gripping my throat.

It was the wail of a single word: "Why?"

A new brand of evil

I first arrived in Baghdad a few weeks before the U.S.-led invasion. A cloud of fear and secrecy gripped Iraq; residents spoke to me in double entendre or slipped scraps of paper scrawled with cryptic messages into my hand.

"What you hear is not true," read one note, secretly given to me after my government minder said all Iraqis loved Saddam Hussein.