Two of the weapons -- the pump-action Remington shotgun and a Glock 9mm handgun -- were purchased legally less than a week ago, on Feb. 9, authorities said. They were purchased in Champaign, where Kazmierczak was enrolled at the University of Illinois.
The other weapons were still being traced.
The gunman's father, Robert Kazmierczak, briefly came out of his single-story house in Lakeland, Fla., to talk to reporters.
"Please leave me alone. ... This is a very hard time for me," he said as he threw his arms up and wept.
He declined further comment, saying he was diabetic. Robert Kazmierczak then went back inside his house, which has a sign on the front door that says "Illini fans live here."
Bush talked by telephone with NIU President John Peters and said people will be praying for the families of the victims and for the Northern Illinois University community.
Campus Police Chief Donald Grady said investigators recovered 48 shell casings and six shotgun shells following the attack in Cole Hall. The gunman paused to reload his shotgun after opening fire on a crowd of terrified students in a geology class, sending them running and crawling toward the exits. He shot himself to death on the stage of the hall.
Kazmierczak, whose first name was earlier listed as Steven, was taking some kind of medication, Grady said.
"He had stopped taking medication and become somewhat erratic in the last couple of weeks," Grady said, declining to name the drug or provide other details.
Correcting information his office released earlier Friday, DeKalb County Coroner Dennis J. Miller said five students, not six, were killed in the rampage, in addition to the gunman. Miller said the higher victim total was the result of confusion over the fate of a patient taken to another county for treatment.
"There was a miscommunication," Miller said.
The motive of the killer, who graduated from NIU in 2006 but was a student there as recently as last year, was still not known. Grady said Kazmierczak was an "outstanding" student while at NIU and authorities were still trying to determine why he would kill. There was no known suicide note.
"We were dealing with a disturbed individual who intended to do harm on this campus," Peters said.
Witnesses said the gunman, dressed in black and wearing a stocking cap, emerged from behind a screen on the stage of 200-seat Cole Hall and opened fire just as the class was about to end around 3 p.m. Officials said 162 students were registered for the class but it was unknown how many were there Thursday.
John Giovanni, 20, of Des Plaines said the gunman calmly fired at the greatest concentration of students.
"He was shooting from the hip. He was just shooting," said Giovanni, who turned and ran so fast that he lost a shoe. "I was running but I was hurtling over people in the fetal position."
Peters said four people died at the scene, including three students and the gunman. The other died at a hospital. The teacher, a graduate student, was wounded but was expected to recover.
Miller released the identities of four victims: Daniel Parmenter, 20, of Westchester; Catalina Garcia, 20, of Cicero; Ryanne Mace, 19, of Carpentersville; and Julianna Gehant, 32, of Meridan.
Another victim, Gayle Dubowski, a 20-year-old sophomore from Carol Stream, died at a Rockford hospital, Winnebago County Coroner Sue Fiduccia said.
The killer had been a graduate student in sociology at Northern Illinois as recently as spring 2007, Peters said. He also said the suspect had no record of police contact or an arrest record while attending Northern Illinois, a campus with 25,000 students about 65 miles west of Chicago.
The gunman was a student at the University of Illinois in Urbana-Champaign, Chancellor Richard Herman said. The university is about 140 miles south of Chicago.
Lauren Carr said she was sitting in the third row when she saw the shooter walk through a door on the right-hand side of the stage, pointing a gun straight ahead.
"I personally Army-crawled halfway up the aisle," said Carr, a 20-year-old sophomore. "I said I could get up and run or I could die here."
She said a student in front of her was bleeding, "but he just kept running."
"I heard this girl scream, 'Run, he's reloading the gun!"' More than a hundred students cried and hugged as they gathered outside the Phi Kappa Alpha house early Friday to remember Parmenter. Flowers, candles and small notes were left in the snow near Cole Hall.
The campus was closed on Friday. Students were urged to call their parents and were offered counseling at any residence hall, according to the school Web site.
The school was closed for one day during final exam week in December after campus police found threats, including racial slurs and references to shootings earlier in the year at Virginia Tech, scrawled on a bathroom wall in a dormitory. Police determined after an investigation that there was no imminent threat and the campus was reopened. Peters said he knew of no connection between that incident and Thursday's attack.