Barker, 42, was at a home near 2nd Avenue and I Street, about one block from his own home, when Taylor spotted him.
In footage from Taylor's body camera, he can be heard repeatedly asking Barker's name, saying neighbors reported his behavior was suspicious. After a brief, relatively calm conversation, Barker can be seen growing agitated and shouting at Taylor.
The encounter went from "zero to 100," as Barker yelled and stuck a finger in Taylor's face, as Taylor later described in a police interview.
As Taylor can be seen in the footage moving forward — to go "hands on" and try to cuff Barker, the officer later told investigators — Barker jumps back and swings the shovel at Taylor, disabling the body camera.
Taylor said he fell off the porch and realized his arm was broken, according to a report released Monday by District Attorney Sim Gill. Taylor said he grabbed his Taser because he couldn't reach his gun. But Barker "jumped on him" and hit the Taser out of his hand, Taylor told investigators.
Barker also grabbed at Taylor's "gun or holster at least twice," Taylor said.
"I know if he gets my gun, he's going to kill me," Taylor said, noting that he was especially concerned that Barker hadn't fled after knocking Taylor off the porch.
"I've had guys fight me, but they run away," Taylor told investigators. "When I got knocked off, [Barker] had plenty of time to run away. He's still coming ... grabbing for my gun. His one goal was to try and kill me."
Taylor said he pushed Barker off him and drew his gun, shooting Taylor three times from a "couple of feet away."
Eyewitnesses supplemented Taylor's account.
Richard Grow, who lives in the northwest corner of the Avenues, witnessed the final moments of the struggle between Taylor and Barker.
Grow, 66, was driving south on I Street when, as he approached 2nd Avenue, he saw the two men leap off a front porch, one after the other. In an interview with The Salt Lake Tribune, he said he is not sure if the officer was the first one off the porch; he initially thought they were two roommates fighting and only later realized that one was a policeman.
By the time Grow pulled up, stopping his car about 40 feet from the fight, the two men were wrestling on the ground in front of the house.
"They wrestled on the ground for 10 to 15 seconds," Grow said. Then he saw the officer "reach around his side and pull out his gun and hold it up to the guy's chest and bam, bam, bam. ... point-blank against this man's chest."
Grow got out and asked the officer, who Grow thought looked haggard, if he needed any help.
"He just said, 'Get out of here,' " Grow said. He obeyed, but filled out a statement at police headquarters a few hours later.