From the article:
A Dundee-Crown liaison police officer initiated the lockdown about 11:15 a.m after finding out that a senior student had threatened in a text message to bring a gun to school, police and school officials said.
Earlier in the morning, the senior was involved in an altercation at the school with another student. The threatening text message followed.
The senior, a teenage boy from Carpentersville, later went home, Carpentersville police Cmdr. Tim Bosshart said. Police said they did not find a weapon on the student when they took him into custody at his home.
Police didn’t release the name of the student, and as of Friday afternoon he had not been charged, Bosshart said.
When the code red announcement was made, teachers closed classroom doors, pulled shut the blinds, and gathered students in a corner of their rooms, said Max Ramirez, a 14-year-old Dundee-Crown student from Algonquin. Students were on lockdown for about 45 minutes, he said..