"I was watching the movie and he came in. I wasn't paying any attention to him and I just saw some of my classmates see the gun and then everything just got really serious," Biehl said in an interview on "Good Morning America" this morning.
Hengel pulled out a gun and shot the movie projector and ordered classmates to hand over their cell phones, police said. He broke his own phone when it rang. He was carrying two pistols and a knife, police said. Additional bullets for the two guns were in the backpack.
Michael Arnold was one of the students Burd turned away from the classroom. "The door was closed, the lights were out," he said. "But as we started going we immediately heard a loud bang."
Nevertheless, officials said the hostage situation wasn't discovered until a parent, who was concerned his daughter had not answered his phone call, came by the school. Lambie said he went to classroom to find the girl, only to be confronted by Hengel.
"The student threatened me with the gun and told me to step back," Lambie said. Hengel was calm throughout the exchange, he said.
Lambie left the classroom, but not before one student -- the daughter of the man that called -- was able to exit the classroom with him.
Immediately afterwards, Lambie said he called the police.
Police set up a command center inside the school. They reached the teacher by telephone, but Hengel refused to talk.
Worried families gathered at the Marinette County Courthouse where they awaited for news from the scene.
"Heartbreaking. Heartbreaking," parent Lura Keller said Monday night. "I can't believe it's happening."
At 7:40 p.m., Hengel released five students who told him they had to use the bathroom.
One of the hostages, Zach Campbell, told The Associated Press that the class tried to keep the gunman calm by talking about fishing and hunting.
"We just wanted to be on his good side," Campbell said.
Campbell said the gunman seemed depressed, but "didn't really seem like he wanted to hurt anybody."
Biehl said the gunman "was just waving the gun back and forth at the ground ... wasn't really threatening anyone."
About 20 minutes later, gunshots rang out and police broke down the door.
"As the officers approached him, the suspect fired one shot and injured himself in a self-inflicted gunshot wound," Skorik said.
No other injuries were reported.
At a news conference today, Skorik praised the students in the class who he said were "remarkably calm in extremely stressful conditions."
Police recovered shell casings from a .22-caliber semiautomatic and a 9mm pistol from the scene.
"The shots were fired into walls, into some objects inside of the classroom. That information will be fleshed out in the hours and days to come, there's still a crime scene analyst there processing the scene," said Skorik.
Seemingly everyone involved, from Hengel's classmates to school administrators, is dumbfounded by his actions.
"He was an outdoorsman. He liked hunting and fishing," Lambie said. "I was unaware of any problems with this particular student. He was a student in good standing."
Students were left wondering why a fellow classmate would resort to this.
"He was a good student, he wasn't talkative in high school really, but he never seemed like he would do something like this," student Kordel Brezsko said.
Classes at the high school were canceled today, but Lambie said school will be back in session Wednesday.
"With what happened yesterday, we understand there is a fear factor, but as the adults and the leaders in the building, we need to take care of our kids," he said. "Students at Marinette High School are safe."
ABC News' Jennifer Metz and The Associated Press contributed to this report.