It was a normal school day until Sarah Everhart and her 300-person lecture heard shouting from outside.

"Get down! Get down!" a police officer yelled.

Police were still investigating reports of a shooting after a gunman had entered the building when Everhart and her fellow Purdue University students were rushed from their lecture hall.

On Tuesday, 23-year-old Cody Cousins allegedly walked into the Electrical Engineering Building basement and fatally shot fellow student and teaching assistant, 21-year-old Andrew Boldt.

Audio usually reserved for easy note-taking captured the tense moment when an economics classroom was evacuated by police in the same building where Boldt was killed.

Everhart, a 19-year-old engineering major, posted an edited version of the audio to her Facebook.

"When we first heard the shouting, we just assumed it was a drug search, or that a kid got too aggressive with a cop," Everhart told the Huffington Post. "No one [seemed concerned about] the yelling."

In the audio, Professor Kelly Blanchard's lecture is interrupted by a police officer screaming, "Get down! Get down!" from outside the building.

"If you guys see anything out there that looks dangerous, let me know and we’ll take off. Be honest,” Blanchard says to nervous laughter.

As the professor continues to teach, she is again interrupted.

“Is that the same thing?” she asks.

Moments later, officers enter the room and ask everyone to evacuate. The recording ends with the sound of a fire alarm blasting through the building.

"It still didn't hit us that much until we walked out and saw there were cops everywhere," Everhart said.

Everhart recalled counting at least eight officers with their guns drawn, some lining the hallways while others faced the basement stairs where the alleged shooter had been moments ago.

The students were escorted from the building into another one. Outside, Everhart said she saw six police cars and multiple ambulances.

Today, it all seems like a blur for Everhart.

"Walking outside right now, it seems like a normal day, even though we know something happened yesterday," she said. "I know people are struggling right now with losing a fellow friend."

Despite the ordeal, Everhart said her professor handled the situation very well, even though no students received a text message alert until after the evacuation.

"[Blanchard] kept her calm, and didn't freak us out, even though she didn’t know what was happening, either," she said. "That was the one good thing."

As students continue to cope with Tuesday's events, Everhart took to Facebook to express her condolences.