LOWELL — The massive gun scare that plunged UMass Lowell into lockdown on the very first day of classes has ended with a stunning twist: the “gunman” who triggered a citywide manhunt was a juvenile carrying nothing more than an airsoft replica rifle.

Police confirmed late Wednesday that the male, described in emergency alerts as a 5’5” Asian male in a sweatshirt and shorts, was spotted near Riverview Suites brandishing what looked like a long rifle. Helicopters, K9 units, SWAT teams, FBI agents, ATF officers, and state troopers flooded the South Campus as terrified students locked themselves in dorm rooms.

But the weapon was a fake. Detectives recovered the imitation gun — a black airsoft rifle that looks nearly identical to the real thing — and determined the juvenile suspect never carried a live firearm.

Superintendent Greg Hudon defended the overwhelming response, saying the department “will always utilize every available resource until the safety of all involved is assured.” He thanked residents and students for cooperating during hours of panic and lockdown.

The incident capped a nerve-shredding day for UMass Lowell students, many of them freshmen moving into dorms for the first time. What should have been a celebratory first day of class instead turned into a nightmare of sirens, alerts, and images of armored SWAT trucks swarming the campus.

While no one was injured, the fallout leaves lingering questions: how could a juvenile waving a replica rifle shut down an entire university and mobilize half the state’s law enforcement apparatus?

For now, UMass Lowell is breathing a sigh of relief — but students and parents remain rattled after a first-day-of-class they’ll never forget.