Police said they haven't determined why Cody Cousins, 23, shot Andrew Boldt, a 21-year-old teaching assistant from West Bend, Wis., inside the school's Electrical Engineering Building about noon Tuesday.
Purdue Police Chief John Cox said witnesses believed the shooting was "an intentional act" but said there was no immediate indication that Cousins and Boldt had past troubles.
No one else was injured, and Cousins surrendered to a police officer outside the building after firing four or five shots, Cox said. Cousins is being held at the Tippecanoe County Jail on a preliminary charge of murder. No hearing has been scheduled, county Sheriff's Department Capt. Denise Saxton said Wednesday morning.
Officials at the university 60 miles northwest of Indianapolis praised the police response, but the shooting left many students jittery.
"I heard a couple (shots) and then I heard a man scream," said sophomore Nick Wieland, who told the Journal & Courier that he was in a classroom adjacent to the one where the shooting occurred. "Then the last few kind of trailed off as I got under my desk. (I was) just very scared. That's what I felt the entire time."
Purdue President Mitch Daniels cut short a weeklong university trip to Colombia and canceled classes Tuesday and Wednesday.
"Violent crime, whenever and wherever it occurs, shocks our conscience and incites our rage. When it happens in our home, to a family member - and as a Boilermaker Andrew Boldt was family to us - those emotions are more powerful still," Daniels said in a statement read Tuesday night at a campus vigil, which was attended by hundreds.
Purdue spokeswoman Liz Evans said the building where the shooting occurred would reopen at noon Wednesday.
A spokesman for Boldt's family in Wisconsin requested privacy as they mourn.
"For the moment their request is simply that we pray. The church is open all day for those who wish to pray in silence or to light a candle for Andrew and his family," said the Rev. Nathan Reesman, Pastor of Saint Frances Cabrini, in West Bend, Wis.
Former teachers described Boldt, an Eagle Scout, as someone who loved robotics and computers and was always willing to help others with technology issues. He spent two summers interning for John Deere in Silvis, Ill., according to his LinkedIn profile.
Jean Morrell, Boldt's calculus teacher at Milwaukee's Marquette University High School, recalled how he frequently stayed after class to talk to her about math concepts, robotics and his dreams of attending Purdue, Morrell's alma mater.
"Andrew Boldt was a young man who had the potential to make the world a better place. He was a phenomenal young man," Morrell said, her voice cracking. "He had a great mind but he also had a great heart. I'm just sad he won't get an opportunity to realize his dreams, to make his contribution to the world."
The Rev. Warren Sazama, the president of Boldt's high school, said Boldt's family was in shock.
"The mother said, 'You don't expect to get up in the morning and expect your son to be one in a million for a tragedy like this to happen,'" he said.
Little is known about Cousins, who Cox said has addresses in Warsaw, Ind., and Centerville, Ohio. Efforts to reach relatives weren't immediately successful.
The Electrical Engineering Building reopened at noon Wednesday.
Purdue shooting victim remembered at vigil
On Tuesday night, Boilermaker pride was on display as members of the Purdue marching band played at a vigil. Students and staff braved the bitter cold to pay tribute to a fellow classmate described as a capable student, but an even better person.
Boldt was in class at the Electrical Engineering Building when police say he was fatally shot by a fellow student 23-year-old Cody Cousins.
"The victim appeared to have been targeted by the suspect no more or less than that," said Chief Cox.
Cousins, an engineering student, was arrested shortly after the shooting. Alex Poerio captured the arrest on his cell phone.
"I started filming because the cop had his gun drawn, the student didn't have a coat or back pack and that was a red flag," said Peorio.
"I can't believe first of all that there was a shooting at Purdue and that the victim is one of our graduates. Right now, we're just in a state of shock," said Jeff Monday, principal, Marquette University High School.
Police said they had prior contact with Cousins during his years on the Purdue campus for an alcohol-related incident.
"This doesn't appear to be what you would typically have as an active shooter on a campus. This individual seemed to have intentions for the decedent, took the actions the individual took, then turned around and left the building and was taken into custody moments after the act," Cox said. "You train and plan, and train and plan for one of these incidents and you hope it never happens, but unfortunately it did today here."
The school was placed on lockdown Tuesday while police responded. The shooting occurred in the basement of the Electrical Engineering Building on the West Lafayette campus. That building was evacuated and the entire campus was placed on lockdown.
"Homicides are extremely rare events at Purdue, it's shocking," said Tim Sands, provost, Purdue University.
"No ongoing threat to campus. Resume normal operations," the university posted to its Twitter feed.
"Getting texts from people, whether from the Chicago area or friends in other places. I got a lot of, 'Are you OK?' People reaching out to me in that way," Bridget Coverick, senior, said.
The Associated Press contributed to this report.