In response police have stepped up their presence at the school, but some parents say it's not enough.
Police say the Neumann Goretti junior asked a female student, "How do you want to be killed? Do you want me to cut your head off or shoot you?"
He also indicated he had a hit list of students. That led to a police investigation and the 17-year-old's arrest on Monday.
Wednesday morning there was an increased police presence outside of Neumann Goretti High School in response to last week's threat.
Parents say they were vaguely notified about it Sunday by the Archdiocese, and some parents were so fearful that they kept their children home to begin the week.
"I think the school is doing everything they can. We might need a little more police presence here. But the school acted quickly and they let us know what's going on," said one parent.
Philadelphia Police Lieutenant John Stanford tells us, "It's a very serious allegation... I mean it's very disturbing. We've seen these types of incidents take place across the country a number of times - one too many times."
Lieutenant Stanford continued, "We haven't actually discovered a list, but according to what we have been able to determine at this point, this young man was speaking to other students, made some indications he was compiling a list of student in which he intended on doing harm to."
Police searched the juvenile's home on the 1300 block of South 33rd Street, and after finding some disturbing items, the boy was charged with making terroristic threats, simple assault and harassment.
"Recovered were a video of this young man playing with a butterfly type knife, in terms of practicing with it. Also I believe a holster - a makeshift holster - and a blade were recovered from his home," Stanford said.
The Archdiocese released a statement that reads in part:
"We have every reason to believe that our school is safe at this time and that the threats originated from and were isolated to one individual."
The Archdiocese also says it has hired a private security company for arrivals and dismissals that will continue through the end of the year.