The Boulder County Sheriff's Office says the first threat was found written on a wall inside the school Monday afternoon.
Rich Brough, a commander with the Sheriff's department, says a hit list of around 30 names was found by students Thursday.
The commander says the note made threats of explosives and bombs. Investigators are meeting with the school officials and families of people on the list.
"We made a recommendation to the school district that they don't have school on Friday for safety reasons, for the students," Brough said. "It gives us more time to do an investigation and see if we can identify who is responsible, and see if the threat is credible."
Thursday night, school officials say deputies used dogs to comb the school looking for bombs. Deputies will monitor the school through next week.
Niwot High School has offered a $1,000 reward for anyone with information about who has been making the threats.
The following letter wassent to parents:
Thursday, January 10, 2013
Dear Niwot High Parents and Guardians:
This communication is an update to the message I provided you early Thursday afternoon, and contains new and important information.
Based on the recommendation of the Boulder County Sheriff's Department, the District will close Niwot High School at the end of the day on Thursday. The school will remain closed Friday and over the weekend.
The recommendation to close the school was made, in part, due to a second written threat discovered by students earlier on Thursday. Canceling school provides law enforcement professionals additional time to evaluate the threats.
Be advised that the second threat identifies the names of approximately 30 Niwot High students. Law enforcement professionals have begun contacting the parents of these students for follow-up discussions and to ensure their student's safety.
At this time, the details related to these events are the subject of a criminal investigation. While the timing and extent of new updates will be impacted by the investigation, I will make every effort to keep you fully informed.
According to criminal experts, threats of this nature are usually made by an individual or a small group that acted out previously but friends and acquaintances chose not to report the incident. For this reason, I urge you to sit down with your student tonight and discuss the seriousness of this incident and the importance of reporting any information that might help us resolve it.
The status of events scheduled for Niwot High during this is as follows:
Niwot Elementary Talent Show practice postponed
Niwot High Girls Basketball v. Longmont High postponed
Niwot High Wrestling v Greeley Central at Greeley Central High School
Niwot High school day canceled
Niwot High Boys Basketball v. Longmont High at Longmont High School
Niwot Elementary Talent Show postponed
Niwot High Gary Daum Wrestling Invitational at Frederick High School
The school schedule for Monday, January 13, is unchanged at this time. I will keep you informed of any changes.
Please do not hesitate to contact me if you have additional questions or information.
Dennis Daly, NHS Principal