After a Chaska teen shot an arrow that struck his friend nearly 100 feet away, he rushed to his side, pulled out the arrow and tried to stop the bleeding. But the victim, 16-year-old Spencer Swanson, died two days later from the head injury.

The new details emerged Thursday when authorities announced that the teen shooter won't be criminally charged in the October death. The conclusion to the more than four-month investigation stunned Swanson's mother, Teri.

"I'm surprised, frustrated," she said. "I don't understand what's the lesson, and how is there a lesson in any of this? ... I mean, you killed my kid. And you have to live with it, but you're walking away, and there's no recourse."

She said she hadn't necessarily wanted her son's friend to serve jail time, but she had hoped that he at least would face some consequence, even if it was just community service.

But Dakota County Attorney James Backstrom, whose office handled the case because of a conflict of interest in Carver County, said they found no evidence that the teen, who isn't being named, intended to shoot the arrow in Swanson's direction or at all.

"It's a terrible, tragic accident," Backstrom said. "Spencer Swanson was unfortunately at the wrong place at the wrong time."

According to his office, the 16-year-old had just recently received a new 50-pound PSE compound bow and arrow and had practiced using it at an archery range once. Around 6:25 p.m. on Oct. 13, the teen had just restrung the blunt tipless arrow to show it to Swanson, who was meeting him to go play basketball at a nearby community center.

The teen told investigators that the arrow was pointed at a tree when he saw Swanson riding his bike down a hill toward him. He told investigators he tried to let up on the arrow to remove it but lost his grip, shooting the arrow about 94 feet and striking Swanson in the forehead.

The teen called police and disentangled Swanson from his bike, pulling out the arrow and putting pressure on the wound to help his friend before police arrived.

For Teri Swanson, the details are hard to believe. The single mother of three said she had lectured her 8-year-old about safety using his own bow in front of the shooter just minutes before the incident happened.

"I'm confused; what has he learned?" she said of the shooter. "I understand we each have to deal with this the rest of our life in our different ways — him, in a different way than we will."

Backstrom said that Chaska police did a thorough investigation and that although they decided it's unlikely the arrow ricocheted after hitting the ground as the teen initially told police, there was no evidence that he intended to shoot the arrow or to shoot it in Swanson's direction.

"It's an extremely unusual tragedy," Backstrom said. "It's hard to imagine this would occur almost 100 feet from where it struck. ... It was a tragic accident by a young man who didn't intend for this to occur, and tried to help his friend."

Swanson, a junior at Integrated Arts Academy in Chaska, was hospitalized and died two days later.

Attorney Marsh Halberg, who represented the shooter, said the teen and his family are relieved by the outcome.

"We hope the healing can now begin from both sides," he said. "Spencer was like my client's brother since they were small; there was a lot of suffering here."

Twitter: @kellystrib