During the tense four hours that Dylan Klebold, 17, and Eric Harris, 18, held Columbine High School in Littleton, Colo., under siege, members of the school community—administrators, teachers, students, janitors and others—demonstrated a heroic selflessness that may have saved countless lives. Along the school's U-shaped science corridor, for example, redesigned five years ago to modernize the wing's labs and classrooms, the department's dozen teachers responded to the crisis with an unwavering determination to safeguard the 227 students in their care. Last week those 12, a close-knit bunch, many of whom have been teaching together for 15 years, and the departmental secretary sat down with reporter Vickie Bane to reconstruct the mayhem that erupted around them. Tears flowed as some heard one another's stories for the first time since the April 20 massacre.

As fifth period got under way at 11:20 a.m., chemistry teacher Theresa Miller, 40, was late for her regular Tuesday assignment as hall monitor. Delayed when she stopped to set up a lab for three students, she now had to hurry through the halls to make sure everyone was where they belonged. As she neared the top of the science wing's stairway, a student raced by her, taking three steps at a time. "I yelled, 'Stop!' but he just kept running," she says. "I remember having the thought, 'I'll remember your face.' " A moment later three boys came from the direction of the library. "One of them said, 'There are two guys down there with guns, and they're shooting everybody.' My first thought was, 'Yeah, right.' Then I heard gunfire."

Miller ran down the hall to the departmental office and dialed the main office. When a student answered, she yelled, "I need to speak to an adult now!"

"They already know, and they're on their way down there," the student responded. Cappi Wyatt, 43, who was grading papers in the biology office, heard Miller report the shooting and simply couldn't believe it. "I just went, 'No way. Not at Columbine.' I thought, 'It's a prank. It's a joke.' " But as Miller headed down the hallway to alert department chairman Frank Petersen, the sounds of screams and gunfire made Wyatt a believer.

As Petersen came out of his classroom, the corridor suddenly filled with hundreds of running students, the only sound the pounding of their feet. Afraid of a stampede, Miller kept yelling, "Slow down a bit!"—until she heard a spray of gunfire. "A bunch of kids hit the ground," she says. "Back behind them, I saw [business teacher] Dave Sanders on his stomach." While Miller corralled the fleeing students into classrooms, computer-tech teacher Rich Long, 52, tried to help Sanders up. Spotting blood in Sanders's beard and on his shirt, Long shouted for Petersen to get help. Petersen sprinted to the main office, where he came upon a group of straggling students and quickly herded them out the front door.

Back in the science wing, many teachers still thought the banging in the hallway was firecrackers or some other senior-year folly. Several assumed the Pop! Pop! Pop! was the work of chemistry teacher Kent Friesen, 48. "When I heard the fire alarm," says Dick Will, 52, "I said, jokingly, 'Guys, they did it this time. They burned down the chemistry room. Out! Let's go!' " He dispatched students along the fire-alarm route, which goes past the library, but they were turned back by Miller's screams of, "There's a gun! Get back in your classrooms!" Will says he and Chris Mosier, 38, "were just grabbing and throwing kids into rooms. We got the halls clear."

In the class where Bev Williams, 53, had allowed a brief breakdancing demonstration before handing out a biology test, a cranked-up boom box had masked the sounds of gunfire. Now, alerted to the danger by Miller, Williams hurried students into the greenhouse adjoining the classroom. "One of the little girls who had come up from downstairs told us she thought she had seen gunmen, and they were shooting and people were falling over," says Williams. That left several students trembling in terror.

As everyone huddled together, says Williams, "we were stroking one another's backs, trying to stay calm." She, like several other teachers, found that lies were the best currency of calmness. Though she wasn't certain, she assured students that the greenhouse door, which opens into the main hallway, was locked. When students became agitated about the safety of their siblings, she told them "what they needed to hear. It never dawned on them that I didn't know any more than they did."

With the halls cleared, other problems arose. For the 60 students and five teachers in the biology classroom of Doug Johnson, 49, the challenge was to keep Dave Sanders alive. Following the example of Friesen, several students stripped off their shirts and threw them to junior Aaron Hancey, an Eagle Scout with first-aid training, who had rolled Sanders into a fetal position and was trying to stanch the bleeding. "Dave was semiconscious," says Miller. "His mouth was filling up with blood so much that he couldn't say much." With his eyes, though, he followed the two students who were assigned to keep him conscious with a stream of patter.

After Hancey established phone contact through his father with a 911 operator, Wyatt began to turn tables on end so that if the gunmen came in, "there would at least be some kind of maze where [the students] could take cover." Johnson, meanwhile, wrote " 1 bleeding to death" on a white board that was propped in the window. Then, avoiding the halls, Friesen went in search of paramedics while Johnson tried to locate the gunmen.

Alerted by gunfire that the assailants were in the science wing, they ducked into a chemistry room, where they joined 20 students and teachers Doug Craft, 53, and Al Cram, 52. After brainstorming strategies on how to thwart the gunmen should there be an encounter, the four teachers removed the room's overhead light bulbs and prepared to blast the gunmen with fire extinguishers. Across the hall, Long and earth science teacher Will, who had 11 students with them, tied computer cables together to secure the door. "We armed ourselves with X-Acto knives," Will says with a smile.

As the minutes ticked by, the students who were crouched together in the greenhouse began to lose circulation in their legs. At one point they heard one of the gunmen shout in a flippant tone, "Today I am going to die!" After the shooting ceased around 1 p.m., the relentless blare of a fire alarm began to grate on people's nerves.

But the tedium was broken by occasional moments of humor. Classmates chuckled when a girl momentarily got her head caught between a helium cylinder and a cabinet. When the 2:30 bell rang and one student said, "Oh, good, it's time to go home," her fellow captives giggled. And, of course, the inevitable arose. "Mrs. Williams," said a girl in the greenhouse, "I've got to pee. I just have to." Williams's students used the sink. In Johnson's room, the receptacle of choice was a lab beaker.

When the students began to get fidgety, earth science teacher Cheryl Mosier, 31, handed out paper and pencils. Some students played hangman and tic tac toe; others wrote letters to family members. Mosier began to compose a letter to her husband and colleague, Chris, but, she says, "I started to cry and knew I couldn't do that in front of the kids, so I switched gears and wrote my prayers."

Around 3:00, SWAT teams began reaching the science wing. "We heard clump, clump, clump coming up the steps," says Williams. "The kids were terrified to open the door. They were so sure that it couldn't possibly be the people rescuing us." Even after everyone was rescued and brought to Leawood Elementary School, teachers put the kids first. Cheryl Mosier felt she had to maintain her composure after husband Chris arrived with students still clinging to him. But when they finally embraced, she says, "I totally broke down and hugged the hell out of him."

Surely the memories will stay with Columbine's survivors for as long as they live. Last week, Williams asked her youngest departmental colleague, Troy Manuello, 27, how he was doing. "I feel old, really old," he answered. Then he said something Williams will never forget: "You know, I got into this profession so I could have an impact on young lives—not so I could save them."