Pennsylvania State Police in Greensburg were called in to investigate three 15-year-old students at Hempfield Area High School.
This after reports that two students had guns in their backpacks.
At a news conference, investigators say it appears it was a case of one student trying to sell weapons to others.
One transaction is believed to have taken place on a school bus, another took place in a bathroom.
Investigators do not believe at this point that the students were planning anything violent at the school.
The school was placed on lockdown for a few hours with students being dismissed about 20 minutes later than normal.