They prepared for guns but faced knives instead.

In the era of Newtown and Virginia Tech and Columbine, danger and bloodshed came Wednesday to Franklin Regional High School not at the end of a barrel but rather at the points of two flashing blades.

Just after dawn, police said, sophomore Alex Hribal went on a rampage through a wing of the Murrysville school in a scene straight from a horror movie, slashing and stabbing 21 students and a security guard with two 8-inch knives. The swift and apparently random attack ended only when an administrator tackled the boy. Within five minutes, a high school hallway was transformed into a bloody crime scene; sleepy students waiting for first period suddenly became victims of violence; and a slender, dark-haired 16-year-old from Murrysville described as quiet and studious, and looking younger than his years, emerged as the latest face of the national epidemic of school violence.

Gov. Corbett praises first responders, teachers, students

Gov. Tom Corbett offered praise to first responders, police, teachers and students in remarks at a news conference today regarding the knife assault at Franklin Regional High School. (4/9/2014)

"When I saw a kid bleeding on the ground is when I realized this was really serious," student Hope Demont said. "It was absolutely mind-blowing."

Four of her peers remained in critical condition Wednesday evening, and Westmoreland County District Attorney John Peck said the incident could yet turn fatal.

"There is a question about whether [one] person will survive," Mr. Peck said during the suspect's evening arraignment before District Judge Charles Conway in Export.

The teen, clad in a blue hospital gown after being treated for minor hand wounds, was charged as an adult with four counts of attempted homicide, 21 counts of aggravated assault and one count of possessing a prohibited weapon on school property. He was denied bail and was taken to the Westmoreland County Juvenile Detention Center in Greensburg.

The charges might not reflect all victims, according to Westmoreland County public safety spokesman Dan Stevens. Two other students were treated for injuries that were not from being stabbed.

Mr. Peck told the court that the suspect made some statements after school officials tackled him that indicated he wanted to die.

Defense attorney Patrick Thomassey described his client as a good student with no prior criminal record and no history of addiction to drugs or alcohol. He said his client is not a loner and interacts well with other students.

Mr. Thomassey described the incident as "bizarre" and asked for a mental evaluation to determine whether his client will be competent for an April 30 preliminary hearing.

"My prayers go out to everyone who was injured today and I hope they recover as quickly as possible," the suspect's father, Harold Hribal, told WTAE-TV outside the family's home on Sunflower Court.

Despite several hours of interviewing the suspect, Murrysville police Chief Thomas Seefeld said investigators had not uncovered a motive.

"We don't know what led up to this," Chief Seefeld said. "We're praying and hoping the best for all the victims."

Hope Demont said she heard rumors that the suspect called an upperclassman earlier this week from a restricted number saying, "I'm going to [expletive] you up."

Asked about that phone call, Chief Seefeld said, "We're checking it out."

Gov. Tom Corbett, appearing at a late-afternoon news conference after clearing his schedule and driving to Murrysville from Harrisburg, asked the question on everyone's minds: "What made him decide to get up today and do this?"

News of the attack attracted national attention and lit up social media as condolences flooded through cyberspace and at least two stabbing victims posted on Twitter pictures of themselves at trauma centers sporting bandages and wearing hospital gowns.

The incident also drew in federal law enforcement. The FBI was at the suspect's two-story house on a cul-de-sac, executing search warrants, seizing a computer and interviewing witnesses. And U.S. Attorney David Hickton pledged his help. He noted one thing that was not seized: the suspect's cell phone -- he said the teen did not have one.

Wednesday began in typical fashion as the high school's 1,222 students entered the building just after sunrise. But by 7:13 a.m., when police were alerted, terrified students would be fleeing for their lives.

It was one of the most vulnerable possible times for chaos.

"Once the students are in the building and in classes we can go into lockdown," school director Roberta Cook said. "But before school starts, it's hard to completely secure the building."

Gracey Evans, a junior from Murrysville, said she arrived about 6:50 a.m. Twenty minutes later, as she stood in a hallway while her best friend stopped at his locker, she heard someone say something about blood.

"I saw this kid in all black running down the hallway, stabbing," said the Evans girl said. "He was just stabbing everybody that was in his way."

Her friend was wounded in the back, she said, and a nearby student was stabbed in the stomach.

The incident began in a classroom in the school's science wing when the suspect pulled out two knives and started slashing and stabbing fellow students, said Mark Drear, vice president of Capital Asset Protection, which provides security guards for the school.

Students, some of them wounded, ran from the room with the suspect chasing them a few hundred feet down a hallway. Many students were still at their lockers; some of them were attacked along the way, Mr. Drear said.

One student who realized what was happening pulled a fire alarm to try to evacuate the school. That caused students who were in other classrooms to crowd into the hallway.

According to a police affidavit, Officer William "Buzz" Yakshe of the Murrysville police, a specially trained school resource officer assigned to the district, was working in his office when he heard a commotion.

He and his office mate, private security Sgt. John Resetar, went to check. The two separated, with Officer Yakshe heading toward the cafeteria and the sergeant going down the hallway against the flow of stampeding students, according to Mr. Drear.

At first, Mr. Drear said, Sgt. Resetar thought the flow of bodies was because of the fire alarm. But then he saw the blood on the students.

"He knew something was wrong," Mr. Drear said. "He saw the gentleman holding knives. When the gentleman saw him he lunged at him. ... He was stabbed and still holding the suspect, trying to get the weapons out of his hands."

When Officer Yakshe returned, the affidavit said, the sergeant was "leaning against a wall and ... bleeding from his stomach."

At that point assistant principal Sam King appeared and tackled the suspect, authorities said.

Mr. King told police that he heard the commotion, ran into the hallway and saw Sgt. Resetar being stabbed.

Both Mr. King and Sgt. Resetar grappled with the suspect, Mr. Drear said. A third private security guard, Officer Ken Wedge, rushed in from outside and saw the pileup.

"He got into it, got the assailant into a choke hold and got him to eventually drop the weapons. They were having a hard time getting them out of his hands," Mr. Drear said.

Sgt. Resetar was treated for a stab wound above the rib cage that did not hit any vital organs, Mr. Drear said. He was released from a hospital.

"That Sam King, thank goodness he was there," Mr. Drear said. "It could have been a lot worse."

Ms. Cook and fellow school director George Harding said the district had done extensive training on how to respond to a critical incident. But most of the training focused on an active shooter, Ms. Cook said, not someone with a knife.

Regardless, the directors said, the practiced response protocol appeared to work effectively as school officials and security subdued the suspect, evacuated the school and quickly sought emergency help for the wounded.

"This is our worst nightmare, but these kind of scenarios, we have discussed them and trained for them extensively with our staff and emergency responders," Ms. Cook said.

The fact that a student pulled the fire alarm, she added, meant that he followed training recommendations to do so in any emergency so that students and staff would know to evacuate.

Although the school is relatively safe, the staff was under no illusions. In a 2013 school yearbook spread on the shooting deaths in December 2012 at Sandy Hook Elementary School in Newtown, Conn., one teacher wrote: "I know that this can happen anywhere. It was sad to see students coming to school with the attitude that something bad could happen."

Franklin Regional has no metal detectors, which is not unusual for a suburban school, according to Linda Hippert, executive director of the Allegheny Intermediate Unit.

"Metal detectors are not as prevalent in the suburban schools as they are in the city schools. Schools in the city are more used to seeing weapons, and that's just the reality," Mrs. Hippert said.

She said she's not certain whether the Franklin Regional incident will prompt more schools to install metal detectors.

"The more important discussion is about why do we have children who are so disturbed that they want to cause this level of harm to their classmate, teachers and others? That's the deeper problem we are dealing with from a mental health perspective," Mrs. Hippert said.

Public officials lauded the emergency response and quick actions of school administrators.

Murrysville Mayor Robert J. Brooks called Wednesday "a day of heroes."

"You don't expect something like this to ever happen in Murrysville," Mr. Brooks said. "Seeing the activity that went on at the schools, the teachers and the kids that pushed each other's out of harm's way, the kids that stayed with their friends and put compresses on. ... It's just amazing."

This story was written by Jonathan D. Silver, based on his reporting and that of staff writers Molly Born, Rich Lord, Liz Navratil, Mary Niederberger, Michael A. Fuoco, Lexi Belculfine, Moriah Balingit and Eleanor Chute.