Olsen's attorney countered that his client, who was a Dekalb County police officer at the time of the shooting, was scared and acted in self-defense.
Jurors heard opening statements Thursday in a trial to decide whether Olsen is guilty of murder. The white former officer fatally shot Hill, a black US Air Force veteran who was naked and apparently unarmed.
Hill's killing led to protests in Atlanta that mirrored nationwide demonstrations over race, policing and excessive force in recent police killings.
Defense attorney Don Samuel argued Thursday that his client didn't have a clear picture of Hill's actions or what his background was. He only knew that people had called 911 scared of a man acting up.
"How does a human being react when you have 6 or 7 seconds and someone is running at you?" Samuel asked jurors.
Police said Hill saw the officer and started running at him as Olsen called him to stop. But within seconds, the officer was drawing his weapon and fired two shots.
Olsen initially had pulled his handgun in an attempt to make Hill stop, Samuel said.
"That's why the gun is pulled out. Not to shoot. But it doesn't work. It doesn't work," the attorney told jurors.
Dekalb County prosecutor Buffy Thomas said Hill never threatened the former officer and didn't touch him.
Witnesses saw Hill "anywhere from five to seven feet from the officer at the time he shot him. He wasn't on top of him, he wasn't touching him, he was five to seven feet," Thomas said.
The prosecutors also questioned Olsen's motivation to fire his handgun. She argued that Olsen could have not been afraid of his safety after seeing Hill naked.
The former office was simply uncomfortable, she said.
"And because he was uncomfortable, his actions in using deadly force were unnecessary. Not only were they unnecessary, they were unreasonable and they were unjustified," Thomas told jurors. "And unfortunately, they cannot be undone."
Olsen is charged with two counts of felony murder and 4 other offenses, including aggravated assault, violation of oath of office and making false statement.