Police in Madison, Wis., are investigating how the 15-year-old school shooter obtained a handgun.

Police Chief Shon Barnes, in an interview Tuesday morning with CNN’s John Berman, said partners at the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) are expediting a trace form “to determine the origin of that weapon, who purchased it, and how it got from a manufacturer all the way into the hands of a 15-year-old girl.”

“These are questions that’s going to take some time to answer,” Barnes continued. “We‘re fully committed to getting the answer to that.”

Barnes said police do not know yet whether the........

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