The police responding to a knife attack in Boise, Idaho, on Saturday night that left nine injured, including six children and three adults.

A man targeted children attending a 3-year-old’s birthday party during a stabbing spree that wounded nine people at an apartment complex in Idaho on Saturday night, the police said.

The man, identified as Timmy Kinner, 30, had returned to the complex, Wylie Street Station Apartments, around 8:45 p.m. on Saturday, a day after he was asked to leave the property because of his behavior, William L. Bones, the police chief in Boise, Idaho, said at a news conference on Sunday.

Mr. Kinner began attacking the children with a knife, said Chief Bones, who was visibly emotional as he described a scene of victims scattered across the apartment complex, in the street and on the walkway.

Among the victims, he said, were the 3-year-old who was celebrating her birthday, two 4-year-olds, a 6-year-old, an 8-year-old and a 12-year-old. The three other victims were adults who tried to intervene. Four victims received life-threatening injuries.

“This was an attack against those who are most vulnerable, our children,” Chief Bones said. “It’s untenable, it’s unconscionable. It’s pure evil in my mind.”

The birthday party, which was complete with cake and decorations, was held outdoors in an area that was accessible to the public, the police said.

Mr. Kinner has not cooperated with officials so the motive of his attack remained unclear.

The complex is home to some refugees…