He is facing nine counts of aggravated battery and six counts of injury to a child.
The complex houses many resettled refugee families, but Kinner is not a refugee.
Esrom Habte, 12, and Fathi Mahamoud, 11, were playing in the grass behind their apartment when the attack began.
"It was kind of scary," Esrom told news media as his mother looked on. "He was chasing people and stabbing people."
"We saw him saying bad words and stabbing a grown-up really hard and a lot of times," Esrom said.
The children ran into an apartment and hid in a closet with other children until police told them it was safe to come out, he said.
Colourful bouquets rested outside crime scene tape the next day.
"This incident is not a representation of our community but a single evil individual who attacked people without provocation that we are aware of at this time," Bones said during a press conference Saturday night.
Police found stabbing victims inside the complex and in the parking lot. Kinner was arrested a short distance away.
Bones said the stabbing resulted in the most victims in a single attack in Boise Police Department history. "As you can imagine, the Wylie St Apartment and our community is reeling from this attack," he said.
The apartment complex is just off of one of Boise's busier streets, separated from the traffic by one of the many irrigation canals that run through the city.
Victim witness coordinators and counsellors were being made available to the victims, their families and friends and other residents of the apartment complex, Bones said.
"Our hearts go out to the victims who are in the hospital tonight, please keep them and their families in your thoughts and prayers," he said.
Boise Mayor Dave Bieter condemned the attack on Twitter.
"Last night's horrific attack does not represent Boise," Bieter wrote. "Please join me in praying for the injured and their families. We must come together to condemn this vile act."
- AP
