John Dewey High School was put on lockdown for three hours Thursday after police say a gun fell out of a male student's backpack during history class.

According to witnesses, the student tried to flee the classroom, but was apprehended around 12:30 p.m. However, police confirmed Thursday evening that they have no suspects in the case and continue to investigate.

Scores of students were lined up outside of John Dewey as officers patrolled the perimeter of 50 Avenue X and a police chopper circled overhead.

Many expressed shock at the latest incident, saying a 15-year-old boy brought a gun to campus earlier this month. Metal detectors were subsequently installed. Thursday's gun incident is raising questions about whether those detectors work and about the school's safety in general.

Click here for team coverage on reaction to the incident.