By Hannah Meisel and Scott Cameron

It’s still not clear what led to yesterday’s altercation between a driver and students outside of Champaign’s Centennial High School. A student protest against the killings of black men Michael Brown and Eric Garner by white police officers ended when a woman drove her car into the center of the rally.

The rally began taking shape early Thursday morning, when a group of students and teachers started organizing a "die-in." That’s when protesters drop to the ground at the exact same moment, in this case holding signs with phrases that read, “hands up, don’t shoot,” and “black lives matter.”

150 or so students thudded to the ground in the school's main lobby in the passing period before the last class of the day.

Students remained immobile for 15 and a half minutes — 11 to represent the 11 times New York man Eric Garner told a white police officer that he couldn't breathe as he was held in a choke hold before dying, and another 4.5 for the number of hours Michael Brown's body lay in the street after being shot by a white police officer in Ferguson, Missouri.

Centennial principal Greg Johnson says after the students found that news media was outside the school, they asked to march outside, and administrators approved.

"They went outside to protest and ... it was about 20 minutes of peaceful protest continued outside, with students doing some chants, and being together, crying, holding each other," he said. "It was really a nice moment for Centennial at that point. But unfortunately, a large number of students began to march south and there was a car coming up north and there was an altercation between the students and that car that was brief but incredibly unfortunate."

Here's a video of that altercation.

In a video obtained by WILL students' chants turn to screams as a car rolls through a group of students at low speed. In the video, one student is seen hitting the car's driver's side window. No injuries were reported, but a student — or group of students — allegedly hit the windshield, causing it to partially shatter.

Champaign Police Lieutenant Bob Rea recounted the incident to WILL, from a report from an officer at the scene.

“The car that sustained the broken windshield, was, in the officer's words, idling through the crowd and the crowd starting smacking on the windshield and one individual busted through the windshield out with it looks like their fist," he said.

Rea says the department is investigating the incident to determine which individuals are responsible, but no charges had been filed as of last night. Rea says the driver was just trying to get through the street and was not ticketed.

But some students tell a different story. They say the driver motored through the crowd while giving them the middle finger.

One student who participated in the rally reached out to Patricia Avery, president of the Champaign County Branch of the NAACP. Avery says she was disturbed by the student’s description of the driver's behavior — though she says she can’t know that driver’s intent. And she says the incident comes at a moment when racial tensions are high.

"When you have this kind of behavior coming from a citizen against a group of students, you're sticking your finger up at a group of kids? I don't know what that is," she said.

Police and the school principal say they have no proof that the driver flipped off the students. And neither the school nor the police are assigning intent to the driver.

Principal Johnson says he's proud of how students conducted themselves, and says Thursday's incident was a lesson Centennial students could never have learned out of a book.