Midland Park Police posted on Facebook that it was investigating along with the Bergen County Sheriff's K9 unit.
All schools in the Midland Park Public School District were put on lockdown Wednesday morning for about an hour after a bullet was found at the high school, the district's superintendent said.
The schools were placed on lockdown at 10:35 a.m. after the "potential safety risk" was found at the high school, said Marie Cirasella in an emailed statement.
Midland Park Police posted on Facebook that it was investigating along with the Bergen County Sheriff's K9 unit.
The lockdown was lifted at 11:31 a.m. and students resumed classes, Cirasella said.
Sara Jerde may be reached at sjerde@njadvancemedia.com. Follow her on Twitter @SaraJerde.