“I am so, so extremely lucky that I was very unproductive at work today,” she said.

Erickson, a Minnesota native who is pursuing a doctoral degree in engineering and fluid and thermal science, explained that she was in her office at the Barus and Holley engineering building until 4 p.m. Saturday. “I was like, ‘Man, I’m just not getting anything done,” she said, “and randomly decided I would go to the gym. I never go to the gym in the afternoon.”

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At 4:05 p.m., a man dressed in black clothing, identified by police as a person of interest, walked down Hope Street and rounded a corner after leaving the scene of the shooting, according to an 11-second video later released by police.

And at 4:22 p.m., the university alerted the campus to an active shooter near the Barus and Holley building, instructing students to lock doors, silence phones, stay hidden and run if they are in the affected area.

“I was leaving the building within five minutes of the shooter coming in,” Erickson said, noting that two students were killed and nine other people were injured in the shooting.

Erickson said that once the alert went out, school officials turned out the lights in the gym where she was and pulled down the shades.

“Everyone kind of sat on the ground, getting tons of texts calls, calling our parents, telling people we love them, texting all of our friends, ‘Where are you? Are you okay?’ ” she said.

Erickson, who has been the female captain of the men’s club hockey team at Brown, said she sat in silence with a teammate in the gym for about four hours before school officials turned the lights back on and told students they were going to be moved.

“There were SWAT teams all over, and they have us take over belongings, register who we are, where we were, get a wristband,” she said. “And they walked us two buildings over to go to the (athletic center.)”

Erickson recorded the video while sitting on the floor at the athletic center. She said she had met up with other teammates who had been at the university’s science library when the shooting occurred. Those students barricaded themselves in classrooms, she said, and police ended up breaking down the doors because it would not be wise to open doors in such a situation.

Erickson said she appreciated the thoughts and prayers that people were sending. “But we need more than thoughts and prayers,” she said. “It’s ridiculous that as college students in America, we have to worry about people shooting up our classrooms.”

Edward Fitzpatrick can be reached at edward.fitzpatrick@globe.com. Follow him @FitzProv.