Unanswered questions remain about a fatal shooting at a Madison, Wisconsin, private school Monday as new details emerge about the upbringing of the teenage girl who allegedly opened fire.

Investigators are working to piece together how and why 15-year-old freshman Natalie Rupnow, who went by the name “Samantha,” allegedly committed the act that left one teacher and a student dead and wounded six others at Abundant Life Christian School, one week before Christmas.

Erin Michelle West, 42, of DeForest, and Rubi Patricia Vergara, 14, of Madison, were both pronounced dead at the scene of the shooting, the Dane County Medical Examiner’s Office said in a news release Wednesday.

Four pe...