Nobody was injured and no suspect or suspects were immediately taken into custody, but the explosion raised concerns among students at South Milwaukee High School after the wave of school violence across the country last year.
"I didn't feel positive that they knew that there were no more bombs," said John Kleineider, a 16-year-old sophomore, who left school before it even started Tuesday. "I just didn't want to take the risk of finding out the hard way."
The school opened on time Tuesday, but got about 125 calls in the morning from concerned parents. Attendance at the school, which has about 1,200 students, was at about 83 percent, about 10 percentage points below what it normally is, Principal Richard Regner said.
The school explosion was reported 1:30 a.m. Tuesday, after nearby residents were awakened by a blast. That was about 11-and-a-half hours after a pipe bomb explosion next to a dumpster outside a South Milwaukee bowling alley and a little more than 13 hours after an explosion in a recycling bin in the nearby suburb of Oak Creek.
"We think that they're related because of the proximity and because of the type of devices and the time frame," South Milwaukee Police Chief Tim Talaska said outside South Milwaukee High School Tuesday, not far from where the bomb had shattered windows and tore through an overhang above the main entrance.
Talaska said police did not know whether children or adults had detonated the bombs. The chief added that there were no threats or notes that came with the blasts.
Police, who were assisted by the U.S. Bureau of Alcohol, Tobacco and Firearms, planned to send any evidence gathered to the state crime lab for analysis, Talaska said.
Bomb-sniffing dogs searched the school and the parking lot before classes started. The dogs did another sweep through the school after students had arrived and found nothing, Regner said.
"Absolutely the kids are concerned," Regner said Tuesday. "We feel the building is as safe as it ever has been and probably safer because of the fact that the dogs did go through this morning."
The main entrance at the high school was closed and blocked off with yellow tape Tuesday. The damage cause by the blast was less than $5,000, South Milwaukee schools Superintendent David Ewald estimated.
Up to 10 South Milwaukee officers were at the school after the blast and adults were placed at each entrance, authorities said.
Some South Milwaukee High School students thought classes should have been canceled, and that the school was not taking enough precautions.
"We are afraid of a Columbine repeat at our school," said student body president Morgan, a 17-year-old senior who came to school anyway to attend a scheduled audtion for the school musical. "There are plenty of students who are dropping out each period."
Others did not seem nearly as worried.
"I don't think it's a big deal," said Pat , a 17-year-old senior. "I don't think it's going to happen again. I think it was a prank because of this Y2K thing."