ST. JOHN'S, N.L. -- The Newfoundland police officer who shot and killed Don Dunphy on Easter Sunday 2015 says he could only think "No!" as he suddenly saw a rifle in the man's hands.

Royal Newfoundland Constabulary Const. Joe Smyth says he braced for impact, convinced he'd be shot.

He told an inquiry Wednesday into the killing that he took his eyes off Dunphy -- contrary to his training -- long enough for him to reach down to the right side of his recliner for the gun.

"By the time I focused on that firearm it was pointed at me. I thought I was going to be shot," he testified.

"I noticed in my peripheral vision that he's leaning down to the right side. As he came back up I noticed something in his hands, long. It was a long barrel firearm and it was very jarring and shocking to see the gun."

"I immediately went to high alert, high adrenaline mode."

"I'm very much thinking 'You're going to be shot. This is going to hurt."'

Smyth said he shouted "No, no, no."

"It was a plea," he said.

"I saw nothing other than that gun. And as I moved toward the door I started shooting."

Smyth said he fired two shots at Dunphy's "centre mass" but the rifle was still pointed at him.

He said he fled the small living room, firing two more shots at Dunphy's head, and saw the last shot make impact.

Smyth fired four shots with his pistol, hitting Dunphy once in the left chest and twice in the head.

A fourth shot missed. Pathology reports indicated any of the three shots could have been fatal. It's believed Dunphy died instantly.

Smyth had gone to Dunphy's home in Mitchell's Brook, N.L., to check out Twitter comments that were flagged by staff in then-premier Paul Davis's office. Dunphy, 59, was an injured worker who'd fought with workers' compensation for years. He blamed the system for his state of poverty.

Smyth has testified Dunphy invited him into the home but soon became agitated as the officer commented on the rundown and "filthy" state of his home. He also refused to sit down on his couch due to cat hair.

"He was very bothered by the fact that I was looking around the house," Smyth said Wednesday.

"What are you looking for? What are you looking around for?" Dunphy repeatedly asked as he became increasingly agitated, Smyth said.

Smyth said he didn't become angry or argumentative with Dunphy -- even as he swore and demanded to know who sent him. He said he appeared to be in an almost "manic" state and "frothed" at the mouth.

Smyth was adamant that Dunphy pointed a rifle at him. He denied staging the scene, as Dunphy's only child, 28-year-old Meghan Dunphy, has testified of her own theory as to what happened.

She said her father always had a metre-long stick at the right side of his chair in case of a break-in, and told the inquiry she suspects her father raised the stick and Smyth mistook it for a gun.

The rifle was found loaded at Dunphy's feet but with its bolt action open. It had not been fired.

Meghan Dunphy testified the .22-calibre rifle had belonged to Dunphy's late father and that she'd seen it just once months earlier behind the couch.

Smyth, who arrived unannounced at the house, called the tampering theory "outlandish."

Commission co-counsel Sandra Chaytor questioned why he would have fired a second shot to Dunphy's head when the first had already caused major damage.

"It's a fairly significant wound isn't it?" she asked.

Smyth agreed the first head injury was "pretty shocking," but said the whole incident unfolded in seconds.

"I was focused on the gun."

In the hours after the shooting, which was in RCMP jurisdiction, Smyth said fellow RNC officers arrived to offer their support at the local RCMP detachment. Although he said he felt ready and wanted to give a statement right away, RNC officers recommended he "sleep on it" to regroup from the intense stress.

Smyth told the inquiry that the statement he gave at 3:30 p.m. the next day was not cautioned -- where investigators warn it could be used in any criminal case.

He said that was "surprising," considering he was the only witness to a homicide.

Smyth disputed an RCMP timeline indicating he waited about 12 minutes after the shooting to call police, saying it was actually two or three minutes.

He also said he deleted a call he started to make right after the shooting to Joe Browne, the premier's former chief of staff.

Smyth said he decided it would be best if Browne heard about the incident from someone else, and he often deleted calls and texts on his phone to create space.

The inquiry is hearing from more than 50 witnesses over the next two months into what went wrong and how to prevent such confrontations in future.