Published: Nov 30, 2010 8:20 PM EST
Updated: Nov 30, 2010 5:22 PM EST

MARINETTE, Wis. (AP) - A 15-year-old boy who held 23 students and a teacher hostage in a Wisconsin classroom died Tuesday at a Green Bay hospital from a self-inflicted gunshot wound, authorities said.

Sophomore Samuel Hengel died at 10:44 a.m. at St. Vincent Hospital, Marinette Police Chief Jeff Skorik said. Hengel, of Porterfield, shot himself as police stormed a classroom at Marinette High School Monday night.

The 24 hostages who were held for several hours Monday afternoon were not injured.

Authorities said they did not know what might have motivated the boy who made no demands or requests during the standoff.

"As far as what caused this, it seems to be a mystery," Skorik said earlier Tuesday. "We have not been able to identify anything that precipitated this incident."

Student hostage Zach Campbell said the gunman seemed depressed, but he didn't think he meant his classmates any harm.

I didn't know really what to think. I was just hoping to get out alive," Campbell said Tuesday on CBS' "Early Show." "He didn't want to shoot any of us."

Campbell told The Associated Press that six of the gunman's close friends were in that class.

--- Associated Press writers Colin Fly and Carrie Antlfinger contributed from Milwaukee; writer Scott Bauer and photographer Mike Roemer contributed from Marinette; writers Kristen De Groot and Jacob Jordan contributed from Atlanta.

(Copyright 2010 by The Associated Press. All Rights Reserved.)