Authorities and witnesses said the chilling encounter began after Reeves grew angry that Oulson was sending text messages as previews rolled inside the cineplex's theater 10.
Charles Cummings, 68, who was sitting nearby with his son, Alex, 34, said Reeves asked Oulson to stop several times, but was brushed off.
Reeves then stormed out of the theater to complain to the theater's management, authorities said.
When he returned, Oulson, who was sitting with his wife, confronted Reeves about going to the staff, and claimed he was sending messages to his young daughter.
The men began to argue, and it got physical, authorities and witnesses said.
"Somebody throws popcorn. I'm not sure who threw the popcorn," Charles Cummings told reporters outside the theater Monday.
"And then bang, he was shot."