A 14-year-old Upper Darby boy has been arrested after allegedly posting at least one threat to shoot students at Upper Darby High School on Friday, police said.

The boy, whose identity was not released, was charged with terroristic threats and harassment by communication after township police entered the teenager's Radbourne Road home with a search warrant Wednesday night, said Upper Darby Police Superintendent Michael Chitwood. Township school officials said they reversed their initial decision to cancel school Friday after they learned that police had made an arrest.

No weapons were found in the home, Chitwood said at a news conference Thursday, and the boy's parents, although "taken aback" at the sudden police presence that converged on their home, were "very cooperative, very decent."

The boy, who is not a newcomer to the Upper Darby School District, was "arrogant" when police confronted him, Chitwood said.

Later, when the boy was taken to the Upper Darby Police Department, police said he confessed to posting a threat to Instagram that said people at Upper Darby High School would be the targets of a shooting rampage Friday. Chitwood said he was not sure why the threat specified Sept. 7, and not any other date, as the day to attack.

The boy's post was identical to a June 29 social-media post Upper Darby police were alerted to at the beginning of the summer, Chitwood said. At the time, an unknown person sent police an email with a picture of the threat, but Chitwood said police were unable to determine who posted the threat on Instagram in June because it had been quickly deleted.

School officials were also not notified of the June threat, Chitwood said, adding that police tried to find out the origin of the threat over the summer, to no avail.

This week, the same threat popped up again on Instagram, Chitwood said. A 15-year-old sophomore at Upper Darby High School who saw the ominous message showed up at the Upper Darby Police Department on Wednesday with his mother to report it.

From there, Chitwood said, police contacted Instagram to push them for information on the user who had posted the threat.

"They gave us the information we needed," he said, "and they were very cooperative in getting us the information we needed to identify where the post was being sent from and who was responsible for sending the post."

Chitwood said Instagram had previously denied Upper Darby police access to user information regarding safety issues.

Around 6:30 p.m. Wednesday, Upper Darby School Superintendent Daniel Nerelli announced schools would be closed Friday in light of the threat. About an hour-and-a-half later, police had taken a suspect into custody, and Nerelli began to rethink his decision to cancel classes.

"We know that in these situations there's always going to be an opportunity for someone to second-guess the decisions that we make," said Dan McGarry, Upper Darby assistant superintendent of curriculum and instruction.

School resumed normally Thursday, authorities said at the news conference, but there would be a heightened police presence for Thursday and Friday at the township's schools. Several of the security guards at the high school are former police.

"School safety is a number-one priority in the nation right now," Nerelli said. "And the thing you don't want to do — which is the situation I have to make a decision with the information we have — you don't want to get copycats thinking they're going to post something on social media to get a day off from school."