(CNN) -- Call it knee-jerk panic or an abundance of caution.
After an eyewitness reported a man with a gun on campus at American University, authorities put the Washington college on lockdown as officers swarmed out to look for him.
In the end, no shots were fired, no crime committed. No one was hurt.
The man turned out to be an off-duty officer from the Metropolitan Police Department.
He was sitting on the bus with a woman he knew -- a student at the university.
Two tense hours
But until that revelation, students already stressed over finals spent two tense hours "sheltered in place" -- as the school asked them to do.
Warnings went out via campus e-mail within seconds of the eyewitness report:
"AU Alert: man with gun seen on campus. Campus is in lockdown. Shelter in place. More info to follow."
The university also sent out the warning via Twitter, and shortly thereafter, photos appeared online on the social networking service showing hundreds of students herded into safe rooms.
Victoria Bera was taking a final when she saw the alert, she told the student newspaper, The Eagle.
"We were really stressed out because we weren't getting the alerts at the same time as other students," Bera said. "We were able to hear the helicopters outside."
The eyewitness saw a man wearing something suspicious and called authorities. They were both riding a campus bus at the time.
"Someone saw a holster, what they believe was a holster, somebody had on them," Lt. Jesse Porter said. But it was enough to put the police on full steam.
"Given the culture we are in now" police thought it was better to start with a massive response and scale back if needed, he said.
"In this time and age, people get concerned."