Newsday reported that the suspect, who was caught in the Bronx, was wanted in connection with a shooting in November of 2011.
The principal of P.S. 4 called for the lockdown as a precaution after police said one child was overheard telling another that he brought a gun to school.
The lockdown was imposed Monday morning after a man called the Warren County communications center around 9:45 a.m. and claimed he was armed with an assault rifle and was in the woods behind Hackettstown High School.
Though the school decided not to close Friday, Smithtown West administrators assured both students and parents that they took the matter very seriously.