San Jose State University students were on lockdown Thursday morning at Sweeney Hall for about 90 minutes after someone called in a report about seeing a man with a gun.
Just before 11 a.m., the lockdown was declared over, and university officials said a "thorough search" of the hall revealed nothing.
That brought a sigh of relief to many students - some whom were were so scared that they initially wouldn't let campus police inside the building to search for the suspect.
About 10:30 a.m., an NBC Bay Area photographer witnessed an undercover femle police officer detaining a man - wearing a black T-shirt, black backpack and jeans - for a time on campus. But he was soon released.
Sweeney Hall - and no other buildings - was put on lockdown before 9:30 a.m., after SJSU spokeswoman Pat Harris said a "credible" report came in about a white man wearing all black clothes, possibly armed with a handgun seen walking near the building in the southwest quadrant of campus near the South Parking Garage on San Salvador Street at Seventh Street.
Students in other classrooms were not asked to shelter in place.
Student Jonathan Aguayo told NBC Bay Area that he saw the man, and it looked like he was carrying a rifle. That man wasn't found.
Student Ashliegh Nikol told NBC Bay email that three police officers came into her class at Sweeney Hall with their guns drawn and were walking down class aisles. One of the officers was overheard telling the professor that they were "looking for a guy with a gun and to stay in class until the alert says we can leave."
Batches of emergency text alerts were sent out; one was issued at 9:22 a.m. campuswide. It read: "Man with gun call - police checking Sweeny Hall - shelter in place."
Other texts were sent in waves, which may explain why on Twitter, some were complaining that they didn't get the message. The university send out many messages, by email, text and Twitter, among others, to keep the community informed.