Lynn Seibel is escorted out of the Rice County Courthouse on Tuesday, Feb. 26, 2013, after his first appearance on 17 felony charges, in Faribault, Minn. A judge set bail at $200,000 with no conditions or $100,000 with conditions. Cristeta Boarini/AP

It was the sound of teenage boys screaming that jolted teacher Seth Hedderick out of his apartment one night in a dormitory at Shattuck-St. Mary's. What he uncovered would remain a secret for years until it surfaced in criminal charges against one of the Faribault boarding school's most beloved teachers.

On that night in the fall of 2000, Hedderick said, he went downstairs to investigate. He passed several boys on the stairs.

"What's going on down there?" he asked.

"N-D-P," one boy said.

The term meant nothing to Hedderick, who had worked at the school for just a few weeks. More students passed. They were naked.

"Where are your clothes?" Hedderick asked.

"It's naked dance party," one boy said. "You can't have clothes on."

"This is over," Hedderick told the boys. "This is not happening."

No, they said, you don't understand. It's fine. "Mr. Seibel's down there."

Lynn Seibel, then 59, was the head of the boys' dormitory and chair of the drama department. The story didn't seem plausible, Hedderick said, but when he entered the basement, there was Seibel, standing in the entrance to the showers, surrounded by naked boys.

"At that point, I was like, OK, this place is screwed up," Hedderick said, "and I walked back upstairs."

Hedderick said he reported the incident the next day to the head of the school, Gregory Kieffer, but nothing was done.

Allegations about Seibel's sexual behavior, including the naked dance parties, remained secret until last year when a former student confided in a probation officer who then called police.

Seibel was arrested in California in August and charged with 14 felony counts of criminal sexual conduct for the alleged sexual abuse of six male Shattuck-St. Mary's students from 1999 to 2003 and three related counts.

Police said Seibel organized naked gatherings where he would coerce boys into sexual activity and offer explicit sexual advice. Students also told police Seibel invited them into his apartment to view pornography, and four former students recounted illegal touching by Seibel when they were alone. Seibel was extradited to Minnesota last week and remains in a Rice County jail pending trial. He did not respond to interview requests.

The school claims it knew nothing of the alleged crimes. Administrators, past and present, declined interview requests.

However, an MPR News investigation has found several teachers and top administrators did know about some of Seibel's alleged sexual behavior but failed to notify police. Hedderick and two other former teachers said they heard rumors about Seibel's sexual interactions with students both while Seibel was employed at the school and in the months following his departure in 2003. Hedderick told two school administrators about the naked dance party, he said, but no one treated it as a criminal matter.

"Lynn, you're a sick man. You need to do something about it."

Seibel even claimed in a recorded interview with police last year that the school knew about much of his sexual behavior, with one exception. According to the criminal complaint, Seibel told police, "I didn't tell [the school] about touching anybody."

Seibel recalled that the school's interim headmaster, Dennis Brown, told him, "Lynn, you're a sick man. You need to do something about it," according to the criminal complaint.

No one considered contacting police, teachers said, in part because allegations about Seibel's behavior, even those reported directly by students, seemed too bizarre to be true, and they assumed police would not investigate rumors.

"It'd be like calling the Ghostbusters on the ghosts that they say are hanging out in the dorm," said Stefanie Tschirhart-Baldwin, a former teacher.

The teachers said they can't recall receiving any training at Shattuck-St, Mary's on how to handle sexual abuse allegations. State law requires teachers to report allegations of suspected child abuse.

"If you're a rational person and you think that you've heard that there's something inappropriate going on, report it," said Faribault Police Chief Andy Bohlen, adding that officers have no knowledge that anyone at the school knew about Seibel's sexual interactions with students.

It's unlikely anyone will face criminal charges for failing to report child abuse allegations because the statute of limitations is three years, with few exceptions.

Hedderick, who now works as an admissions director at a public school in Maryland, wonders whether he could have forced the school to intervene.

"That's something that has bothered me since all this happened," he said. "If I had not accepted their party line, if I had not accepted their incompetence, if I had kept pushing this issue, I feel like there could have been a better resolution to this."

"IT BECOMES A FAMILY"

Seibel's alleged abuse was so widespread and involved so many victims that it raises questions about how it could remain a secret for so long. One explanation may lie in the school's private and close-knit environment, which former teachers said Seibel exploited to gain access to students.

Visitors to Shattuck-St. Mary's pass through a massive stone arch that opens like a picture frame onto a snow-covered courtyard. Students dressed in the Shattuck uniform -- khaki pants, school-crest polo shirts -- stroll from dorms to class. It's an unusual sight in Minnesota, a state that has only five boarding schools.

The iconic archway leading into the campus of Shattuck-St. Mary's, a private college preparatory school in Faribault, Minn., in an undated file photo. Photo by Jackson Forderer for MPR

Shattuck-St. Mary's, founded in 1858, is best known as a hockey powerhouse that helped shape the careers of athletes such as Minnesota Wild player Zach Parise. More than 400 students from grades six through 12 attend the school. About three-fourths of the students live on campus, where the annual tuition is $40,450.

Dozens of teachers and administrators live on or near the campus. Each student residence has several "dorm parents" who live in apartments inside the dorms. Dorm parents coax tired teenagers out of bed in the morning and turn out the lights at night.

"It becomes a family. It's the school up on a hill," said Tschirhart-Baldwin. "For the most part, it's your own little city, your own little world."

Looking back, teacher Todd Arneson, who worked in the dorm with Seibel for two years, views the culture differently: The same qualities that made Shattuck-St. Mary's seem safe also made it vulnerable to predators.

"It was almost a situation tailor-made for somebody to come in and say, 'Geez, half my work is done for me already, and I'll just keep rolling with it,'" Arneson said.

He wonders if the insular culture of the school dissuaded others with direct knowledge of Seibel's behavior from notifying top administrators.

"I think people feel that, 'Hey, if I want to keep my job here, then doggone it, I guess I have to agree, or I can't disagree publicly,'" Arneson said.

The exclusion of police may be another explanation for the secrecy.

This undated photo provided by Rice County Sheriff's Office shows Lynn Seibel. Seibel, a former teacher at a Faribault prep school who is charged with having sexual contact with six teenage students appeared in a Minnesota court Tuesday, Feb. 26, 2013 where a judge set bail at $200,000. AP

In a statement to MPR News, the school said it investigated allegations of sexual misconduct involving Seibel in 2001.

The internal review failed "to substantiate any criminal activity," and the school said it reported the allegations to the Faribault Police Department in "conversations between June and October" 2001.

However, police said they have no record of the conversations, and Shattuck-St. Mary's declined to provide documents or other proof that it reported the allegations when asked by MPR News, citing the ongoing police investigation.

In 2003, Seibel left Shattuck-St. Mary's. He told police that he left because the school knew of his sexual interactions with students, according to the complaint.

School authorities also found child pornography on Seibel's work computer, police said.

The new head of school, Nick Stoneman, confronted Siebel about the pornography in July 2003 right before Seibel left, according to the criminal complaint.

Prosecutors charged Seibel with possession of child pornography last year after the state Bureau of Criminal Apprehension examined the images and found they were "without question illegal child pornography."

The school's statement contradicts the police account. It claims that Seibel left because he violated its code of conduct in a way "that is unrelated to the allegations in the October, 2012 complaint."

The school wouldn't discuss Stoneman's involvement in Seibel's departure. It also wouldn't say how Seibel violated its code of conduct or whether Seibel was fired or asked to resign.

There is no record that the school reported the child pornography to police.

Seibel portrayed himself to students "as the person that takes care of the kids and that the rest of us are crazy, evil adults who are out to get them."

INSIDE THE DORMITORY

Seibel entered the Shattuck world in 1992 when he was hired as a drama teacher. Seibel and his family moved into an apartment in Whipple dormitory, a three-story residence for high school boys, where Seibel served as a dorm parent and later as head supervisor.

In the classroom, Seibel founded an "elite audition-only acting troupe," according to his resume, "whose performance tours included New York City, Scotland and England." He received the school's teacher of the year award in 1993-1994, according to his resume, and cast himself in the lead role in a school play.

"He was revered by students," said Max Prokopy, who served as a dorm parent in the same building as Seibel from 1998 to 2000. He recalled being struck by Seibel's charisma and charm.

"He would be one person whose door was literally always open, and students would be in there at all hours of the night talking to him about their problems...," Prokopy said.

Seibel supervised an all-male dorm where sexualized behavior among students was common, said Prokopy, who attributed the behavior to a locker-room mentality among students, many of whom also played hockey together. Teenagers walked around naked, joked about sex and dared each other to perform stunts like streaking through the girls' dorm.

"You shower together. You live together. You know everybody's business, and it's just not that big of a deal," he said. "Occasionally kids would get in a shower fight and they'd come running out, and [Siebel] would just point and laugh."

Prokopy said he never saw Seibel engage in any inappropriate behavior with students.

NEW TEACHERS VIEW SEIBEL WITH SUSPICION

In the summer of 2000, after Prokopy left, two new teachers moved into the dorm: Hedderick and Arneson.

Hedderick said the dorm was chaotic.

"It was almost 'Lord of the Flies' kind of mentality," he said. "It was woe to somebody who was not big and strong enough to take care of themselves. It was disturbing."

Seibel rarely enforced rules and allowed students to sneak into the building through his apartment late at night, both men said.

Arneson said he thought there was something wrong with an older man who wanted to spend most of his time with children and always seemed to show up when boys were naked.

"I can easily see people viewing that as, 'Yeah, he's so friendly, he's so nice, you know, his door is always open,'" said Arneson. "But I wasn't buying it."

There were also disturbing rumors.

Arneson said he heard from other teachers that Seibel would approach naked boys in the shower or bedroom and comment on the size of their genitals. He said he didn't report the allegations to school administrators or police because he viewed them as just rumors.

Instead, Arneson said, he focused on enforcing rules in the dorm but faced opposition from Seibel, who wasn't concerned about whether students went to bed on time or kept the dorm quiet during study hall.

"It really made it difficult for me as a new teacher and dorm parent at the school, where now I was battling against this culture that was there," he said.

Arneson said he never saw Seibel sexually abuse or touch any students and never heard any rumors that Seibel sexually assaulted anyone. He left the school in 2008 and now teaches English at a private school in St. Louis, Mo.

More rumors about Seibel circulated among teachers in the months after Seibel left in 2003.

Hedderick said a student told him Seibel used a ruler to measure students' genitals.

"I just thought the kid was sort of screwing with me," Hedderick said. "It was just so bizarre. It's like, who does that? I mean it's just insane."

Hedderick didn't report the allegation to anyone, he said, because he couldn't believe it was true.

"I felt like these are these big, tough hockey players, that they're not going to let some crazy old man touch them," he said.

"A CLASSIC PREDATOR"

Hedderick said Seibel portrayed himself to students "as the person that takes care of the kids and that the rest of us are crazy, evil adults who are out to get them."

In retrospect, he said, Seibel's approach may have allowed him to manipulate students.

"He's a classic predator in that way," said Hedderick. "He created this sense of himself as the guy to be trusted, and then he betrays that trust, and the kids can't turn to anyone else because we're all out to get them."

Seibel offered a similar explanation to police in August. "I exploited my authority and I exploited their trust, um, it seems."

Hedderick said he complained about Seibel's lax discipline throughout the 2000-2001 school year but nothing was done.

One of the most disturbing incidents, he said, took place near the end of the school year. He said students in the boys' dorm went into a "flat-out revolt" after being grounded. Boys ran screaming down the halls.

Hedderick ran to investigate and found a teacher in a hallway surrounded by three naked boys dancing.

"It was like that dance from 'Where the Wild Things Are,'" he said. "It was really bizarre. They were yelling at him, calling him fat, throwing food at him. It was really awful."

The teacher appeared to be in shock and said nothing. Hedderick said he yelled at the boys to return to their rooms.

Seibel then came out and intervened.

"'You can't talk to the kids like that,'" Seibel said.

Hedderick immediately decided that he'd never again work in the dorm with Siebel. "And I just went back up to my apartment and then I was done with that."

Hedderick said he told Kieffer, the head of the school, about the incident the next day. The school responded, Hedderick said, by either expelling or suspending the students.

It would be Hedderick's last year in the dorm with Seibel. Hedderick said he considered resigning because of his concerns about Seibel but agreed to stay when Kieffer suggested Hedderick move out of the dorm.

About one year later, Seibel also left the dorm and moved with his family into a house on the edge of campus, said Arneson, Hedderick and Prokopy. No one interviewed for this story could explain why Siebel moved.

Hedderick, who became an assistant principal at Shattuck-St. Mary's, said the lax environment started to change in 2002 when the school hired a new upper school principal, Todd DeRegnaucourt. The new principal was disturbed about the naked dance parties and Seibel's failure to enforce rules, Hedderick said, and worked hard to change the culture by holding students and dorm parents accountable.

About a year later, in 2003, Seibel abruptly left.

"Nobody knew that he was going until he was gone," Arneson said. "It happened, and boom, that was it."