A male UC Merced student stabbed four people with a large hunting knife on the campus Wednesday morning before he was shot and killed by university police, authorities said.
The victims' injuries do not appear to be life-threatening, officials said.
The suspect's identity is known to authorities but had not been publicly released because they were still trying to notify his family, said Merced County Sheriff Vern Warnke.
He spoke at an afternoon news conference where university and law enforcement officials described a chaotic chain of events that began in the Classroom and Office Building near the center of campus.
The attack began just before 8 a.m. in a second-story classroom, when the suspect stabbed a student, Warnke said.
Byron Price -- a 31-year-old employee with Artisan Construction who was working with two colleagues on a renovation project in the building -- heard chairs crashing and screams from the classroom down the hall, his father, John Price, said in an interview.
Byron Price thought there was a fight and went in to stop it, his father said.
Warnke, who did not use Price's name, said the construction worker "stumbled onto" the stabbing and that his entrance probably saved students' lives. Warnke did not go into detail, citing the ongoing investigation, but called his actions "heroic."
After stabbing the student and Price in the classroom, the suspect fled down a flight of stairs, trying to injure others as he ran, Warnke said. The assailant injured another student outside the building and then approached a female university staff member seated outside, stabbing her multiple times.
The staff member was "sitting, literally minding her own business," Warnke said.
Two campus police officers chased the suspect and shot him on a pedestrian bridge on campus, said UC Merced Chancellor Dorothy Leland.
The eight- to 10-inch, fixed-blade hunting knife was found within four feet of the suspect's body, and he was carrying a backpack, according to the sheriff. Authorities said they would search his room and that the FBI was involved in the investigation.
The assailant was described as a California resident from outside Merced County who lived on campus. Warnke said the Sheriff's Department had no prior contact with him.
Two of the victims were airlifted to hospitals and all were conscious, according to the school.
"Their injuries, thank God, appear not to be life-threatening," said Leland, who called Wednesday "a sad and tragic day."
Student witnesses have been undergoing "very comprehensive interviews" by authorities, and some had tried to administer first aid to the wounded, she said.
"Both our police and students acted in a way that would make all of us very proud," Leland said. "This was a tragic event, but the person who caused this event will no longer be able to cause an event like this in the future. The children are safe here."
The campus was closed after the attack and is expected to reopen Friday. School officials have offered counseling to those who want it and shuttles to people who need transportation.
"I can tell you that we're really shocked and saddened by this," said Lorena Anderson, a school spokeswoman. "We're doing everything we can to contact family and parents to make sure everyone here is safe and secure."
Anderson said the crime scene included the building, "the whole center of campus," and the pedestrian bridge across a canal that divides the campus in two.
Officials said they were trying to determine a motive.
Angela J. Yi, an 18-year-old freshman, was attending her morning writing class on the second floor of the Classroom and Office Building early Wednesday when she heard yelling from a classroom down the hall. It was a man's voice. Then came loud footsteps.
"It sounded like someone was running," Yi said. "My professor went out to see what went on, and when she came back inside she was in a serious mood and told us not to leave the classroom."
She and her classmates were calm, she said, because they didn't know what had happened. Police arrived and taped off the classroom where the stabbings occurred, and she left, grateful that none of her classmates were injured.
On Wednesday afternoon, Shayan Rostami, a 19-year-old freshman, read a text message from a classmate aloud as he walked with a group of friends to Lake Yosemite, near campus.
"Dude, I'm shaking," the message read, according to Rostami. "In a million years I never thought it would happen on our campus."
Lois Vincent, an 18-year-old freshman, looked around at the rustling oaks and the Sierra mountains in the distance.
"There's birds chirping, the wind is blowing and you want to think, 'life goes on,'" he said. "But it happened. And it hurts. And, I don't want to be that guy, but it's going to feel different. How do you protect yourself?"
Daniel Garcia-Ceja, a UC Merced junior, said he was walking to class Wednesday morning and ran into a police barricade at the Scholars Lane Bridge.
Garcia-Ceja, 21, said friends who were in the area at the time told him that a person with a knife was shot and killed on the bridge. They said they saw the assailant approaching students with a knife.
"Some of my friends wanted to cry. Some were upset. Some were in shock. It was insane to hear that this happened in general," Garcia-Ceja said. "You know it's happened at other universities, and you know schools have been through these situations ... but I don't think anybody would have assumed it would happen here. We knew it could happen, but nobody thought it would."
Garcia-Ceja had a morning class at the Classroom and Office Building. He described it as a large lecture hall with a mixture of classrooms.
He usually comes to class an hour early to study for quizzes but slept in on Wednesday. He would have been at the building at the time of the attack had he followed his normal routine, he said.
Garcia-Ceja said the campus was largely on lockdown and that students were gathered in small groups talking about the stabbing, trying to figure out what had happened. Like many others, he turned to social media to try to get updates, he said, but there was a lot of confusion.
His brother, Martin Garcia-Ceja, who graduated from the college in 2014, said there was a stabbing on campus a few years ago that was believed to be gang-related. He said he was at a friend's dorm when another student ran past, bleeding. The campus was shut down and the suspect was apprehended, but there wasn't a lot of talk about it afterward.
Martin Garcia-Ceja, 23, of Ontario, said the campus was very open and easy for both students and nonstudents to access.
"We were told our campus was safe, that security was everywhere, but no one really knew," he said. "We were under the impression that we were always safe, but when that [prior stabbing] occurred, we understood that maybe we should take more serious precautions."
About 6,700 students attend UC Merced. The school opened in September 2005 as the 10th campus in the University of California system, with a dedicated mission to increase college attendance in the San Joaquin Valley. The school is one of the biggest employers in Merced County, with more than 1,300 employees.
Anderson, the school spokeswoman, said the campus "is like a little family."
"We're small," she said. "A lot of us know each other really well. It's shocking. You hear about it at other places and you hope to God it's not going to happen on our campus."
Serna and Branson-Potts reported from Los Angeles and Marcum from Merced.