The inferno at School No. 1 may have started by mistake.

On Friday afternoon, more than two days into a siege at the red-brick campus, Russian officials reached a modest agreement by phone with the hostage takers. A civilian truck carrying four unarmed men was permitted to enter a courtyard to retrieve several corpses decaying in the summer sun. The guerrillas sent an armed sentry to observe the work, but he did not appear menacing, according to elite Russian soldiers watching the scene.

"After the first body [was loaded], something happened," said one of the soldiers, who said he was positioned 44 yards from the school. "There was an explosion inside. We didn't start shooting."

The guerrilla seemed equally startled. "He was shocked himself," the soldier said. "Then the shooting started. There was so much shooting all over the place."

Inside the gymnasium, where about 1,200 hostages squatted on a basketball court, the explosion shocked Nadezhda Gurieva, a history teacher who huddled with her three children. She said the guerrillas gave no indication of an imminent confrontation. She and other survivors would conclude that the bomb went off by accident.

Gurieva's 11-year-old daughter fell dead in the first explosion and her son Boris, 14, was seriously wounded. "I thought he was dead but then I touched his cheek and he moved his fingers," she said. But she was unable to move him. She grabbed her third child, 9-year-old Ira, and her niece, and fled to the nearby cafeteria.

A fuller picture of the siege and its devastating ending emerged Saturday. This account is based on interviews with former hostages, including several being treated at a hospital in the nearby town of Vladikavkaz, and with five members of an Interior Ministry SWAT unit that was present at the school. The soldiers spoke on the condition that they not be identified because they did not have permission to speak to reporters.

"The storm was not planned," one soldier said, using the common Russian word for an assault. "We didn't get any orders."

"We were confused," another Interior Ministry soldier said. "We didn't know when to shoot."

From the first major explosion Friday afternoon to the moment the shooting subsided 13 hours later, at least 340 hostages, including 150 children, were killed by bullets, bombs and fire. Another 700 people were wounded, many seriously. A disaster swept over the hostages without remorse, taking toddlers, teenagers, parents and teachers, and savaging the heart of this town of 30,000 people.

A Doomed Celebration

Sept. 1, the first day of school, is known here as the Holiday of the First Bell. In the schoolyard, students were lined up by grade just before 9 a.m., as parents and townspeople waited for the school's youngest pupils to march into the assembly. Music was playing. The first graders carried flowers for their teachers, a Russian tradition.

Gurieva, the history teacher, was giving some last-minute instructions to her students in the 11th grade, who were to perform a dance after the grand entrance. The school director had her speech in hand.

The guerrillas, numbering between 30 and 40, arrived in a GAZ-66, a large military truck with a tarp covering the bed, according to soldiers from the Interior Ministry. They were well equipped, carrying night-vision goggles, sniper rifles, and silencers as well as an arsenal of explosives.

"They were well prepared," one of the Russian troops said. "They were preparing for a long time."

Barking orders, the guerrillas hustled the crowd into the gym. A number of people were shot in these first moments as they resisted or ran. The body of one man was dragged into the gym by his legs after most people were inside -- an example, the guerrillas said, according to survivors.

"Sit down, sit down," the guerrillas said in Chechen-accented Russian, according to survivors. None of the former hostages interviewed said they heard Arabic spoken, despite official accounts that Arabs were present. The survivors described a number of their captors as "Wahhabis," a reference to the Wahhabi sect of Islam originating in Saudi Arabia, because of their long beards and prayer caps. The fighters, including at least three women, were led by a man they addressed as Colonel who communicated by phone throughout the siege, witnesses said.

The space in the gym was so tight that people were literally piled on top of one another. Gurieva said one of the guerrillas told her that they had only expected to find about 300 or 400 people at the school.

Some of the hostages were wounded, many were hysterical, and babies in the crowd had already begun to wail. The guerrillas seized phones and cameras from the hostages and repeatedly screamed at the crowd to quiet the crying children.

The hostages were never sure how many guerrillas there were. One woman, about 50 years old, first appeared on the second day to shout at the crowd that it was time to pray. "They told us to pray to Allah," said Fatima Alikova, 27, a photographer who had gone to the school for the local newspaper. Two other veiled women, pistols tucked into the suicide-belts around their waists, disappeared after the first day, and were not seen again. Some in the crowd whispered that they had blown themselves up, Gurieva said.

Immediately, the guerrillas began building defenses. They set up two large explosive charges connected to a pedal mechanism beside the feet of two sitting guerrillas. They placed mines among the crowd and at entrances and announced that they would explode if touched. Five more mines were hung from a wire that was run between the basketball hoops and over the sitting crowd.

About 22 men were soon removed from the crowd and taken to classrooms. There they broke off the doors and pulled out the desks and chairs to build barricades around the gym and in an adjoining hallway. Those men never returned to the gym, witnesses said. Gurieva said that when she went to the bathroom with some children a couple of hours after the siege began, she saw them lined up with their hands behind their heads. The men were executed, according to Russian officials.

One of the terrorists taunted the hostages about the missing men. "Do you think 22 bodies is enough?" he said, according to Gurieva.

Tamara Galastyan, who was sitting with her daughter and two grandchildren, said she saw one man executed about an hour after the siege began. "They put a pistol to his head and killed him," she said. She said she also saw the body of another man who was killed early on the first day. "They shot one man right away. I just saw him lying on the ground."

Desperation Sets in

As the hours progressed, the heat in the unventilated gym became unbearable. Some children fainted, other vomited, and people began to strip to their underwear. "My grandson said, 'Raya, Raya, I'm so thirsty," said Raisa Tavaseyeva, whose 10-year-old grandson, Elbrus, uses a diminutive to address her.

Some of the elderly were dragged to a room off the gym as they began to fail. One 82-year-old veteran of World War II was ordered to turn his jacket inside out so that his war medals, which were put on for the ceremonial occasion of the school opening, were not showing.

There was no consistency in who got water; it depended on which guerrilla accompanied hostages to the bathroom. Some of the guerrillas forced hostages to crawl to the bathroom and then fired into the roof to hurry them back. Over the 52 hours of the siege, gunfire was frequent, most of it directed at the roof simply to scare the hostages, survivors said.

Conditions deteriorated by the hour. Gurieva was allowed to drink in the bathroom when she accompanied young children there, but many others were not even allowed to go. They were forced to soil themselves.

By the second day, people began to urinate in plastic bottles and then drink from them. "They gave us bottles like this," said Galastyan, pointing to a plastic soda bottle, "and the children had to piss in them and drink from them."

"People exchanged bottles of urine and poured urine on the children to keep them cool," said another woman, Alla, 24, who was with her 6-year-old son, one of the first graders, who lay injured in the hospital. "They didn't allow people to get up."

The guerrillas spoke to the hostages mostly to taunt them. "Do you know why I cut my beard?" said the man the other guerrillas addressed as Colonel, according to Gurieva. "So I can pass your blockades."

"No one cares about you," said the man, who was wearing a traditional Chechen cap over military fatigues, and who Gurieva estimated was about 40. "Not your President. Not your government. You are not needed."

One of the guerrillas carried a video camera and "constantly filmed us," said Gurieva.

A brief moment of hope swept the crowd on Thursday when Ruslan Aushev, a former president of the Russian republic of Ingushetia, entered and said "We are doing our best for you." He was able to arrange the release of 25 people, including mothers with infants.

But desperation soon set in again. "I wrote a letter of goodbye to my mother," said Vika Guseinova, a teenager now barely conscious and lying on a gurney in the hallway of the intensive care unit in a hospital in Vladikavkaz.

Then, at 1 p.m. Friday came the explosion, and panic.

Within seconds, fire crept up the walls of the gym where plastic murals were hanging. Part of the roof began to collapse. Gunfire came from all directions, including from local vigilantes interspersed with Russian troops, and quickly, a second large explosion was set off as one of two large devices the terrorists had placed in the gym detonated.

Some of the hostage-takers began to fire at the hanging mines. The entire roof collapsed.

Gurieva, wounded and in a hospital bed, recalled the moment she left her daughter's body and her 14-year-old son, who was still breathing.

"I couldn't carry my son, and my daughter was dead," she said, crying for the first time in a long interview. She turned to her sister by her bedside. "I should have stayed," said Gurieva, who does not know where her two oldest children are. "I think I should have stayed."

Gurieva took her younger daughter and a niece to the cafeteria, where a guerrilla who followed them forced them into a corner. But when he fired a rocket-propelled grenade out the window, the recoil knocked him unconscious. Another guerrilla ran in and was shot as the group of hostages in the canteen, including the school's cook and gym teacher, scrambled out a window and into the arms of swarming Russian troops.

Galastyan lost her 30-year-old daughter, Anna, and her 10-year-old granddaughter, Satina, when the roof collapsed. "My daughter, her head fell on my shoulder. I screamed, 'Can you hear me? Can you hear me?' She didn't say anything." Her 9-year-old grandson, Misha Mkrtchan, survived.

She saw other hostages with their heads and legs torn off. Her nose was broken and she had burns on her stomach and arm. She was soaked in blood and had to push through bodies to get out. Blood pooled in her ears kept her from hearing, she said.

Tavaseyeva forced her grandson Elbrus under a bench and was lying on top of him when another hostage, a man, grabbed her and led her to a door. Her grandson survived.

Death Toll Still Rising

Outside the school, the chaos was magnified. Armed civilians, many of them toting hunting rifles, converged on the scene. "They only got in the way," an Interior Ministry soldier said. "The only good they did was pull out the wounded. There were so many of them. They were so aggressive, it was impossible to push them aside." Adding another layer of confusion, he said, some law enforcement officers were in civilian clothes.

It took at least four hours for soldiers to enter the school. When they got in, they found a deadly maze of barricades, booby traps and obstacles. "All the bottom floor was barricaded with desks and chairs," said a soldier. "There was a sniper and machine gunner on the bottom floor." One militant was caught before he could detonate a bomb, he said.

After Interior Ministry troops were informed that there were no more survivors inside, they opened fire using grenade launchers and tanks positioned 150 to 200 meters away. The tank fire finished off the roof. It is unclear if everyone in the rubble of the gym was, in fact, dead.

The soldiers accused police of doing a terrible job of crowd control. Some guerrillas donned civilian clothes to attempt to escape by mingling with the crowd. One guerrilla tried to get through with a wounded man, but special forces stopped him, the soldiers said, adding that they personally saw two captured guerrillas.

One guerrilla was set upon by civilians and killed. "People got a hold of him and just tore him apart," said one of the soldiers. But the soldiers noted that the crowd's hatred was blind and they attempted to kill a Russian prosecutor, mistaken for a guerrilla.

By late Saturday morning, the death toll was still rising. In the intensive care unit at a Vladikavkaz hospital, a 2-year-old boy known only by his family name, Daurov, was surrounded by doctors and nurses. His mother, father and sister were in critical condition in other hospitals, doctors said. Shrapnel had sliced through his chin and into his chest. Another piece struck his liver.

His blond curls were brushed back from his pale forehead, and his tiny body was perfectly still except for his chest, which heaved as an artificial respirator pumped air into his lungs.

A doctor turned away from the bed.

"He's already dead," he said. A nurse stroked his hand in farewell.

Relatives cry over the body of Zaur Gutnov, an 11-year-old boy who was killed during the seizure of School No. 1 in Beslan. Relatives try to comfort a woman who identified one of the slain hostages at a morgue in Vladikavkaz, the town where survivors were being treated.