Yantis was shot and killed by Adams County deputies on November 1 after his bull was hit by a Subaru on U.S. Highway 95 outside of Council.
A family member who witnessed the shooting told the Idaho Statesman that Yantis aimed his rifle at the bull's head before he was shot.
"Law enforcement should be trained to de-escalate situations", said Rowdy Paradis, Mr Yantis's nephew.
The deputies were planning to shoot the injured bull, but when the armed Yantis arrived, all of them fired their weapons, investigators say. "In this case, I stood 10 feet away and watched two deputies escalate the situation and needlessly kill a man".
The announcement comes only days after a town hall meeting between residents and the Adams County Sheriff's Office became contentious with residents questioning the transparency of the agency regarding their investigation into the fatal shooting.
Taylor, the Yantis family attorney, said deputies had shot the bull but failed to kill it, and that the animal ultimately died a couple of hours after its owner was gunned down.
That's when a deputy grabbed Yantis' shoulder from behind, turned him around and pushed the rancher.
As well as questions about police use of force, the case has ignited debate about Idaho's long-standing open range laws, which, under certain conditions, absolve livestock owners of liability in cases of road accidents. The sheriff's office hasn't said anything about what happened next, other than that firearms were discharged by both deputies and Yantis.
"There was no shootout". Paradis said he did not see Yantis or the deputies speak. Reports said that his wife, Donna, who was at the scene after bringing Mr. Yantis his rifle, suffered a heart attack and taken to the hospital.
The Spokesman-Review reported that FBI investigators will investigate whether the deputies used excessive force or intentionally shot Yantis.
State police say their investigation will take at least two months to complete.
"ISP will be thorough, the Federal Bureau of Investigation will be thorough", Olson said.
Idaho State Police is also conducting an investigation and the state Attorney General Lawrence Wasden will serve as a prosecutor.