Cooper's gun, which she has owned for about 20 years, was legally purchased and properly registered, Amormino said.
On Tuesday, Cooper relived those terrifying moments at a news conference called by sheriff's officials, who played the 911 tape.
Cooper was accompanied by her husband, a World War II veteran who will be 86 next week. Bob Cooper lied about his age to enlist early and was sent to Europe, he said.
At the news conference, a soft-spoken and composed Cooper said she was amazed by the anger in her voice - and the curse words she let fly - after she fired the shot.
"I am a Christian woman and I'm very proud of it and I don't curse, but after I shot, rage took hold and I just blasted away," she said. "And, in fact, afterwards my husband said, 'I've never heard you talk like that!' "
The stunned intruder apologized to Cooper after she fired, she recalled, telling her, "I'm sorry, ma'am. I'm leaving. Please don't shoot."
Cooper, a self-described tomboy who has also studied archery and knife-throwing, said she has owned guns since she was a teenager but had never fired at a person.
Her husband, for his part, was unfazed by his wife's actions.
"I'm not surprised at all, not one bit," he said, chuckling. "I know her capabilities and what she can do if she has to."