Faisal Mohammad, a computer science and engineering major from Santa Clara, California, began stabbing people Wednesday morning in a freshman general education class in which he was enrolled.
Mohammad was angry because he' had been kicked out of a study group, said Warnke, dismissing speculation that the freshman could have been motivated by anything political.
"There is still nothing to indicate anything, and I mean anything, that this is other than a teenage boy that got upset with fellow classmates and took it to the extreme," the sheriff said.
The note was recovered from Mohammad's body during an autopsy. It included names of specific students, Warnke said.
Mohammad apparently "had far greater intentions to do harm," the sheriff said, because his backpack contained zip-tie handcuffs, two clear bags of petroleum jelly, a night vision scope, a safety hammer to break windows, and two rolls of duct tape.
Warnke said Mohammad wrote about his plan to handcuff students and ambush a responding officer to get his gun. The petroleum jelly was apparently meant to squirt on the floor to cause people to slip.
"We now have a motive and we do know that he had a script that he was going to try and follow, and the very fortunate part is that didn't follow through for him," the sheriff said, praising the efforts of students and others. "His plan went haywire because people fought back."
What was in his backpack
Twenty FBI agents assisted local authorities in the investigation into why Mohammad stabbed two students, one staff member, and a construction worker shortly before 8 a.m. Wednesday as classes began.
"During the course of their investigation, they have found nothing in this person's history, personal belongings, electronic devices, or any other items to suggest anything other than this was an act of an individual for a vendetta," Warnke said.
"There is nothing to indicate that there is any political or religious motivation pertaining to what he did yesterday," Warnke said.
Investigators, who continued their work Thursday, also spoke with the student's parents, who live in the Santa Clara area, according to the sheriff.
Federal agencies continued to assist in the investigation.
"There was absolutely nothing they could find that would indicate he was doing anything other than being a college student at UC Merced," Warnke said. "There was zero radar on this fellow."
Andrew Velasquez is one of three UC Merced students who shared a dorm suite with Mohammad, and he described his roommate as someone who "didn't talk much," Velasquez told CNN affiliate KFSN.
"Every time I would try to say something, he seemed like he'd just ignore it," Velasquez told the station.
"I never saw him walk with anybody" to class, he said.
About Mohammad having been the attacker, Velasquez said: "Why would someone want to do that? I just didn't expect it to be him."
Shortly after Wednesday's stabbing, investigators entered Velasquez's dorm room and asked him to leave, the student said.
A Fresno County bomb squad is testing a substance found in Mohammad's backpack, authorities said.
As of Thursday morning, one of the student victims remained hospitalized, but is expected to recover, the school said.
The staff member suffered a collapsed lung and had surgery, the school said.
The construction worker and other student victim were treated and released Wednesday, the school said.
The campus, 130 miles southeast of San Francisco, is scheduled to reopen Thursday afternoon so faculty and staff can access their offices, except the Classroom and Office Building where the stabbings began, school officials said.
Classes, however, remain canceled Thursday and will resume Friday.
It's not known what relationship, if any, existed between the assailant and the victims, said James Leonard, a school spokesman.
Mohammad entered a classroom in the Classroom and Office Building about 8 a.m. carrying a hunting knife with an 8- to 10-inch blade and stabbed one of the students, authorities said.
The construction worker, thinking it was a fight, went into the classroom and "ended up stumbling upon the stabbing in progress. I think, through his actions, that he ended up saving this student's life," Warnke said Wednesday.
Outside the classroom, the suspect attacked a female staff member and slightly injured the second student, Warnke said.
The suspect fled the building and was chased by two police officers, said UC Merced Police Chief Al Vasquez.
"When the suspect turned toward the officer, an officer-involved shooting occurred and the suspect succumbed to his injuries," Vasquez said.
Warnke said the bomb squad was called as a precaution because the suspect carried a backpack.
"Events like this happen elsewhere, but not at UC Merced, which may be still small in student body but large in its sense of community -- yet, it has happened," Chancellor
Dorothy Leland said in a statement
on the school website. She said the injuries to stabbing victims were not believed to be life-threatening.
UC Merced, which opened September 5, 2005, is the newest campus in the University of California system and is near Yosemite National Park.