(CNN) -- A northeast Wisconsin high school where a 15-year-old sophomore held his classmates and a teacher hostage for about five hours is expected to reopen Wednesday.
The standoff at Marinette High School on Monday ended when the student, Samuel Hengel, turned one of his guns on himself as officers approached, police said.
He died the following day.
Authorities have interviewed the student's parents but do not yet have a motive.
"We may never truly know why this happened," Marinette County District Attorney Allen Brey told reporters Tuesday. He pledged to provide a complete report on the incident.
Hengel was well-liked, had no prior law enforcement contact and "was a good student," said Marinette, Wisconsin, Police Chief Jeff Skorik.
The school plans on making counselors available.
School officials also plan to review the incident and ask if anything could have been done differently.
"If there are some things we could improve upon ... you can be assured we will be implementing that," said school Superintendent Tim Baneck.
Authorities are now trying to determine where the teen got the weapons and how he managed to get them into the school, Skorik said.
"Five or six" shell casings from both of Hengel's weapons -- a .22-caliber semi-automatic and a 9 mm semi-automatic -- were found in the classroom, Skorik said.
Bullets for those weapons also were found in Hengel's pocket at the hospital, and a duffel bag left in the classroom contained "numerous live rounds," he said.
A knife also was recovered, police said.
Officials believe Hengel did not bring the duffel bag into class, but asked to use the bathroom, then went to his locker and retrieved it, Baneck said.
Hengel apparently ordered everyone in the classroom to give up their cell phones. The teacher used a land line telephone in the classroom to communicate with hostage negotiators, said Principal Corry Lambie.
Police entered the classroom, on a below-ground level, after hearing three gunshots Monday. However, based on witness accounts as well as the shell casings, authorities believe Hengel also fired the weapons "prior to police arrival and prior to the school being aware of the situation," Skorik said.
It appeared the student did not aim at anyone, however, he said. Bullet holes were found in a desk and in some audio-visual equipment in the classroom.
Marinette, a town of about 11,600 residents, borders Lake Michigan about an hour's drive north of Green Bay, Wisconsin.
Marinette High School has about 700 students in grades nine through 12.