The course, said Carter-Black, focused on the connection between human behavior and the surrounding environment, and met once a week for three-hour sessions. Each class contained around 30 students, and Carter-Black said Kazmierczak always interacted with his peers well during group work, and participated regularly in class discussions.
Toward the end of September, Kazmierczak withdrew from Carter-Black's course to take a job in the prison system, and became a part-time student. In January 2008, Kazmierczak returned to full-time status.
Despite advising him on his courses on mental health issues, Carter-Black said she never noticed anything out of the ordinary about Kazmierczak, and added that he "looked like all the other students."
Carter-Black said she had no knowledge of Kazmierczak's medical history or treatment.
Kazmierczak grew up in Elk Grove Village, a suburb of Chicago, Ill. He was a 'B' student at Elk Grove High School, where school district spokeswoman Venetia Miles said he was active in band and took Japanese before graduating in 1998. He was also in the chess club.
In Elk Grove, he worked as the Pirates Cove Children's Theme Park in 1995. According to the park's director. He had an acceptable employee record.
Kazmierczak had been a student at NIU in the spring of 2007, where he had majored in sociology and served as an officer in at least two student groups. He had been studying at the University of Illinois-Champaign most recently, according to NIU school officials.
Law enforcement authorities told ABC News that Kazmierczak had likely planned the assault on the school for at least five days. All four guns involved in the NIU shooting were purchased legally from the same Champaign, Ill., gun dealer, ABC News has learned.
The Remington shotgun and the Glock 9 mm were purchased Feb. 9, 2008. The Hi Point 380 was purchased Dec. 30, 2007 and the SIG Sauer 9 mm was purchased Aug. 6, 2007, from the same gun dealer.
Authorities were still checking where he obtained two other pistols, a 9 mm Sig Sauer and a Hi Point 380.
He brought the shotgun in a guitar case, police said, and hid the others underneath his jacket.
In a disturbing twist, authorities report Kazmierczak purchased ammunition from the same Web site as the Virginia Tech gunman.
At approximately 3:15 p.m. Thursday, Kazmierczak — dressed in black and armed with three handguns and a shotgun — entered an introductory geology class and opened fire.
While students ran for cover and hid under their desks, Kazmierczak wounded 16 people, killed five others and then himself.
"The assailant began firing into the assembled class from the stage — from the front," NIU president John Peters told ABC News.
"It didn't seem like he was aiming. He just raised a gun and shot immediately," said Paul Sundstrom, a student who was sitting in the class with his brother Kevin when the gunman opened fire.
Police are investigating the shooting, searching for a motive. They say Kazmierczak left no note. They did find a laptop computer, but the hard drive had been wiped.
What set Kazmierczak off and why he chose his former school remains a mystery.
The Associated Press contributed reporting to this story, with additional reporting by ACB News' Luis Martinez, Emily Friedman and Marcus Baram.