This is the second evacuation for the middle school this week due to a bomb threat.
On Monday, the middle school was evacuated after "bomb today" was found written on a soap dispenser in a boys' restroom, Hoover said. The school, which has 750 students, was evacuated about 1:30 p.m. to the high school gymnasium.
"In that situation, we have the three students that were responsible," Hoover said of the three middle school males who have been suspended since Tuesday for the bomb threat.
The students were caught by surveillance cameras right outside the restroom, Hoover said.
On Wednesday, Greencastle-Antrim High School was evacuated after the message "bomb" was found on the bathroom stall of the upstairs girls' restroom.
"We have no leads at this time," Hoover said.
The message gave no indication of the time or place and was found by a teacher at the high school, Hoover said.
The teacher reported the threat around noon to high school administration and after they investigated it, the police were called, Hoover said.
The high school of 900 students was evacuated Wednesday shortly after noon, Hoover said.
"We made an announcement that we were going through a normal fire drill," Hoover said.
Hoover said some parents came to pick up their children, but "the vast majority did stay."
The Greencastle Police Department notified Pennsylvania State Police in Chambersburg of the bomb threat and K-9 bomb detection units were brought in with the Capital Police of Harrisburg, Cumberland County Sheriff's Department and Cornwall Borough Police in Lebanon County.
"The police finished at 5:30 p.m.," Hoover said.
The school district is considering making up the lost instructional time Dec. 21, when schools are scheduled to have early dismissal, Hoover said.
Security also will be increased around restrooms in the middle and high school.
"What happens now is we have to restrict bathroom use," Hoover said.
Hoover said the three incidents are not related.