School shootings, mass killings are 'contagious,' study finds
By Ben Smart, Special to CNN
Updated 2247 GMT (0647 HKT) November 3, 2015
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Photos:Worst mass shootings in the United States
Parents wait for news after a shooting at Marjory Stoneman Douglas High School in Parkland, Florida, on Wednesday, February 14. At least 17 people were killed at the school, Broward County Sheriff Scott Israel said. The suspect, 19-year-old former student Nikolas Cruz, is in custody, the sheriff said. The sheriff said he was expelled for unspecified disciplinary reasons.