Chris Klemchuk was driving his moving van by the school moments after an SUV struck and killed seventh grader Burgess Hu, a classmate of Klemchuck's daughter.
"Immediately I could see the bike underneath the truck and, I could, they already had, you know, the little boy covered up and I could tell it was, it was not good," he said.
The 12-year-old Hu was apparently riding against traffic on the shoulder of the road when a parent who had just dropped off her own kids made a right turn and hit Hu.
"She felt that she had struck some sort of object and immediately pulled over the right shoulder. That's when she realized she had struck a child that also attended her children's school here," said California Highway Patrol Ofc. John Fransen.
The accident happened just before 8 a.m., minutes before the first bell. School administrators immediately notified students about what happened and brought in grief counselors.
"The children are very sad. The whole school was brought together, again, extremely sad. The young boy was very popular and well known," said Byron schools Superintendent Debbie Burnette.
Klemchuk said he and others would see often see Burgess riding his bike to school from his home in Discovery Bay.
"He rides his bike every day. Everybody knows that child. You know, there's a lot of traffic coming in and out of that school every morning. So, it's not a place for a boy to be riding a bike, I don't think, but still you should be cautious in watching for the children. You know what I'm saying?" he said.
While the CHP investigates the accident, school administrators say counselors will be back on campus Tuesday to help students cope with the loss of a classmate.
Investigators don't believe speed or alcohol was a factor.
Monday night a vigil was held at Hu's old school in Discovery Bay. The crowd lit candles, sang songs, and said goodbye to one of their own.
Classmates are planning another vigil at Excelsior Middle School Tuesday night.