One person in particular, engineering student Jon Meis, confronted and tackled the shooter as he attempted to reload his gun.
Meis, a senior, is a volunteer at the security desk in Otto Miller Hall.
"He saw the guy and got his pepper spray, sprayed him and tackled him," said Meis' friend Patrick Maguire.
Maguire said he's not surprised that Meis didn't hesitate to put his own life in danger to save others.
"I could have been one of these people that was injured or in critical condition," he said. "A lot of (students) were in that building and he stopped him in the lobby. He didn't get any farther than that. I'm grateful for him yeah."
Meis wasn't the only student who stepped up to stop the violence. Blake Oliveira found a pipe in his physics classroom and stood next to the door with another classmate -- fearing the gunman might try to come inside.
"Eventually the cops came in through another door from another classroom, since they're connected, and they escorted us out," Oliveira said.
Meis was taken to Harborview Medical Center, but he is expected to be okay. His friends are relieved and proud of his heroic actions.
"He had a lot to live for and he just acted quick," Maguire said. "I owe him a beer. A lot more people wouldn't be here if he hadn't done that."
Another student security monitor said the shooter came in through the public entrance of the hall. She said staff had prior security concerns in the building because it's located between the canal and Nickerson Street and it's the most exposed building on campus.