For months, it has troubled Maged. Since his neighbor disappeared mysteriously last September, the Iraqi engineer has worried that his friend was locked up in the local prison of the Iraqi secret police.

So, braving streets still crackling with gunfire, Maged turned up on this afternoon at the Al Hakemiya detention center in Baghdad's middle-class Karadeh neighborhood. Maged, 52, was desperate to answer the question so many are asking: What happened to the vanished thousands of Iraq?

"One of our neighbors, we think he's still here," said Maged, an English-speaking man in a neat golf shirt and slacks. "Maybe they [prisoners] are without food. I'm telling the [American] soldiers for three, four days. My colleagues say under this area, there is a tunnel."

Maged is one of hundreds of Iraqis who have dared to start poking into the prisons and police stations of the toppled Iraqi administration, buildings abandoned by security forces just before the U.S. military captured Baghdad. Anxiously, the families venture into deserted jails such as Hakemiya, searching cells, examining documents, calling out in hopes of an answer which, in Maged's case, did not come.

They are people such as Ali Abbatsa, 43, who was jailed briefly and, he says, tortured at Hakemiya in October because of a relative's involvement in anti-government activities. During his 20-day incarceration, Abbatsa says, he caught a glimpse of the relative in another cell. Today, he was back searching for him.

Also, looking was Khalid Issa Ahmed, 40, a taxi driver. He said his brother, a physical therapist, got off the bus near his office in northern Baghdad Dec. 30 and hasn't been seen since. Ahmed suspects that his brother, Mawfak Issa Ahmed, 47, could have been detained because of his work several years ago with U.N. inspectors enforcing the trade embargo. "It's four months we are looking for him," Ahmed said. He, too, had heard the rumor of a tunnel beneath the Hakemiya prison.

"There are too many jails," he sighed. "We need to bring the Marines to search the jails."

Western human rights groups say that the government of Saddam Hussein had one of the world's worst human rights records, with perhaps up to 200,000 people "disappearing" into his secret prisons, based on accounts by Iraqi defectors and others. Some prisoners languished for years before emerging; most were never seen again.

Maged said his neighbor vanished Sept. 15 after he was summoned by the government passport office. The neighbor, also an engineer, had applied for permission to leave the country.

"He came here," said Maged, pointing to the passport office, across the street from the Hakemiya jail run by the Mukhabarat, or secret police. "And he didn't come back."

Neighbors, friends and relatives all made discreet inquiries. But even the missing man's brother, a police official, couldn't learn his fate, Maged said. In a signal of continued nervousness about sensitive political topics, Maged declined to provide his last name and the vanished neighbor's identity.

Like many Iraqis, Maged was frightened to even glance at an office of the notorious secret police during Hussein's rule. So his trip into the jail today was a shock. The tan concrete complex had been trashed like other government buildings, its large picture of Hussein torn down, its halls awash in paper forms, wires, even the cloth ties used to bind prisoners' hands.

Maged, a few friends and five young Marines quickly set to work, plumbing stairwells, poking their flashlights into cells, checking patios.

In one room, Maged started clapping. It was a signal, he said, to the hidden prisoners.

"Maybe they will hear us and say something, yell 'Help!' " he said.

He went onto a terrace and peered over a flooded patio. "Aku ahad?" he called. Is anybody there?

The Marines said their platoon receives three or four requests a day from Iraqis seeking help in finding their vanished relatives.

"They keep telling us they [prisoners] are down here," said Sgt. Matt West, 21, from Elgin, S.C. "There have been so many different stories, you don't know. . . . I just saw a family this morning at a police station. The mother was looking through records, trying to figure out what happened to her son. It never stops."

Maged was eager to press on. "Can we go to the basement?" he asked. The soldiers informed him it was flooded. Maged and the soldiers continued through the building, discovering a staircase hidden in a corner. They climbed it and found a row of cells, dark even in the middle of the day.

Maged slid open the small panels on the doors, which had apparently had been used for providing meals.

"Aku ahad? Aku ahad?" he asked. Is anybody there?

Silence. The search was producing nothing.

That had also been the experience of Abbatsa, who traveled from his home in Mahmudie, about 30 miles outside the capital, to peek into Cell 24, where he remembered spotting his relative, Jamal Abdul Wahab Muhamad, or Prisoner No. 724. The prison was so dark Abbatsa had lit a wad of paper, creating a torch to see down the corridor. He gazed into the small, primitive cell, with its concrete slab for a bed and tiny bathroom area.

"I'm very, very sad. I believe he has been killed," he said.

Ahmed had no luck, either. Strolling around the outside of the prison, he peered into basement windows, discovering only a kitchen. An inspection of the pavement around the building turned up no evidence of a jail or underground space.

The missing man was one of seven brothers, Ahmed said. "He was the only one very quiet in the family." He left, shaking his head dejectedly.

After an hour's search, the Marines had turned their attention from the hunt for Maged's neighbor to some looters attempting to cart off furniture from the jail offices. In a hushed tone, Maged revealed to an American visitor that one of the friends searching with him was the missing man's brother, an important police official. His name was Walid.

He was not giving up.

"Still, I have a little hope," Walid said.

An Iraqi man inspects a cell at the jail where, in the past few days, U.S. Marines have helped people search for relatives or friends they believe might still be held. An Iraqi man, who asked not to be identified, holds up a discarded prison uniform at the Hakemiya jail in Baghdad, where many of his relatives and friends were held.