Vincent fired three shots and Fairbourn was struck in the chest and abdomen.
According to a letter from Salt Lake County District Attorney Sim Gill to West Valley City Police Chief Lee Russo, Vincent "reasonably believed that deadly force was necessary to defend himself ... we conclude that Officer Vincent's use of deadly force was justified under Utah State law."
Fairbourn, who has been described by police as a transient, was charged earlier this month in 3rd District Court with first-degree felony attempted aggravated murder, along with assaulting a police officer, interference with an arresting officer, carrying a concealed weapon, failure of a pedestrian to yield and disorderly conduct.
According to charging documents, Vincent saw Fairbourn acting strangely as the man walked in traffic at 3500 S. 3200 West.
When Vincent approached Fairbourn, the defendant displayed a large, fixed-blade knife, which he refused to drop when ordered, according to charges.
Fairbourn then stepped toward Vincent and was ordered to stop. Vincent then shot Fairbourn.
A witness told police that Fairbourn was 3-5 feet from the officer when he saw Fairbourn grab his stomach, as a result of being shot, according to charges.
Police said the gunshot wound didn't completely stop Fairbourn. When a backup officer arrived, he saw Fairbourn on the ground, propped up on his elbow and saw the large knife on the ground next him.
Fairbourn then rolled on top of the knife and tucked his arms under his body, police said.
It took five officers to get Fairbourn under control, and he had to be strapped to a gurney in order to be transported to the hospital for treatment.
A scheduling hearing for Fairbourn is set for Jan. 31 before Judge Vernice Trease. Bail has been set at $50,000, cash-only.