The motive for a shooting that killed a teacher and a student and wounded others at a Wisconsin school appears to be a “combination of factors,” a police chief said Tuesday as he appealed to the public to share what they might know about the 15-year-old girl who attacked a study hall before shooting herself.

Investigators were still working on Wednesday to determine why a teenage girl opened fire two days ago at her private Christian school in Madison, Wisconsin, killing a fellow student and a teacher before taking her own life.

As vigils in Madison honored the victims of the Abundant Life Christian School shooting, police pushed to identify a motive for the attack.