Buying a gun is a relatively speedy operation in most of the US. Joe Raedle/Getty Images
A mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida, left at least 17 people dead and 14 injured. The suspected attacker, a former student of the school, allegedly used an AR-15 rifle that he had bought legally. In some parts of the US, you can walk into a store and buy a gun within minutes.