CHARLOTTE, N.C. -- Tuesday was the last day of classes at UNC Charlotte, but inside professor Adam Johnson's anthropology classroom it was the first day of final presentations.

• Johnson says he ushered students out of the classroom and into a large courtyard
• Unfortunately, not all of the students were able to evacuate
• He says the shooter was enrolled in his class, but he eventually stopped coming and withdrew

Students were getting ready to talk about everything from drug abuse to animal testing to video games and violence. But as described in a chilling essay posted Thursday by Johnson on his website, seven minutes into the first presentation, life changed.

"Without warning, earsplitting bangs ring throughout the room off the glass walls, creating a terrible reverberation," he said. "Students, in great confusion, begin to run."

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Johnson says he ushered students out of the classroom and into a large courtyard. Eventually he's able to grab a few students and run into the anthropology department. While this is going on, they are yelling "active shooter."

"The students that I have in the room with me are expressing different emotional responses: crying, disbelief, shock," he wrote.

Unfortunately, not all of the students were able to evacuate. Survivors told Johnson the shooter said nothing and started to fire. Eventually, he says a student who has been named as Riley Howell, tackled the shooter who emptied the magazine, laid the gun, down, and sat on the ground.

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One victim, Johnson says, then asked the shooter to stop shooting and he responded "I'm done."

Johnson doesn't use any names in his essay. He also says the shooter was enrolled in his class, but he eventually stopped coming and withdrew. Johnson’s essay is a chilling account.