When Reeves returned to his seat "additional words were exchanged" and Oulson threw a bag of popcorn at Reeves, the report said.
After officers read him his rights, Reeves told the detective that Oulson struck him in the face with an unknown object, and that's when he removed a .380 caliber gun from his pants pocket. The report said Reeves fired the gun and struck Oulson once in the chest and that he "was in fear of being attacked."
Oulson's wife, who was also in the theater, had put her hand on her husband's chest prior to the shooting in an attempt to shield him. Officials say she was also struck by the bullet.
There were about 25 people in the theater at the time of the shooting, witnesses and authorities said. The movie playing was "Lone Survivor," about Navy SEALS in Afghanistan.
"I can't believe people would bring a pistol, a gun, to a movie," said Charles Cummings, who was sitting near Oulson and Reeves. "I can't believe they would argue and fight and shoot one another over popcorn. Over a cellphone."
Cummings, who said he was a combat Marine in Vietnam, said Oulson fell onto him and his son. When they spoke to reporters on Monday, both had blood on their clothes.
"Blood started coming out of his mouth," said Alex Cummings. "It was just a very bad scene."
Charles Cummings said his son went to call 911, while Cummings and another patron who was a nurse began performing CPR on the victim.
The man sitting next to the suspect happened to be an off-duty deputy from another county, and he grabbed the gun out of Reeves' hand, and the suspect did not attempt to get away, Cummings said.
Oulson and his wife were taken by ambulance to a Tampa-area hospital, where Chad Oulson died, said Sheriff's Office spokesman Doug Tobin. His wife's injuries were not considered life-threatening.
Tampa Police spokeswoman Laura McElroy said in a news release that Reeves was a captain when he retired from the department in 1993. She added that he was instrumental in establishing the agency's first tactical response team. After he retired, Reeves worked security for the Busch Gardens theme park and was on the board of a neighboring county's Crime Stoppers organization. Reeves' son also is a Tampa officer, police said.
Follow Tamara Lush on Twitter at http://twitter.com/tamaralush.