Brandon Stehl, 19, who completed high school early but was in the gym for the graduation rehearsal, said he thought the shooting was a senior prank initially.
"It was scary; at first, I didn't think much of it, but then my heart rate sped up and people were rushing out," he said. "I come back to school for one day, and this is something I never thought would happen; I wish it wasn't real."
Stehl said he knows Milby and described him as "hot-headed and reckless" but not someone who was bullied or had emotional issues.
Neither Kylie nor Brianna know Milby well, nor did they know the reason for his expulsion, they said.
"He seemed like a really nice kid, but then everything changed and he was angry and high all the time," Brianna said.
Kylie said Milby has a reputation as a troublemaker.
"It's just too bad that it had to be one of our graduation classmates," Kylie said. "It's just so sad that it happened, especially in such a close-knit community like Dixon."
Students have had some active shooter training, but it was focused mostly on what to do if they were in a classroom, Kylie said.
Still, "I think that we were all prepared, and we had our natural instincts. I think everyone did an amazing job of following directions and doing what they had to do.
"It's such a scary reality that we had to live through ... but people were there for each other, and we all came together as a student body. We all did a really good job coming together, and I think in the face of such adversity, we handled it well. "