Authorities evacuated an elementary school in Utah after a caretaker discovered a bomb on the roof.
Experts detonated the pipe bomb using a high-pressure water cannon after they found it at Mountain View Elementary School in Layton.
The caretaker who found the bomb took it from the roof and told the school principal.
"Why he did that and where he took it, we're not sure. He put himself in a dangerous situation," school district spokesman Christopher Williams said.
There have been no threats made to the school or any other school in the district. This is the first time a bomb has been found on the property.
On Friday, a caretaker was on the roof retrieving a ball but did not see the bomb.
"That doesn't mean it wasn't up there. As to who may have placed it up there, we have no idea at this point," Williams said.
Layton Police are looking into the incident along with the Davis County Sheriff's Office bomb squad.
Dogs trained to sniff for bombs were released into the school on Monday but did not find any explosives.
Maintenance workers were asked to inspect roofs at all of the district's schools.
Despite the high level of stress involved in the situation, Williams said the school handled it well.
"We drill a lot for fire, intruders, disasters. That means when there's a real situation like today, everything goes smoothly. Under the circumstances, things went as well as they could," Williams said.
This comes as America is on high alert about terrorist attacks after the Boston Marathon last week, which killed three people and injured 180.
Yesterday, Canadian authorities said they derailed an al-Qaeda-backed terrorist plot involving a New York City passenger train.