On March 15, 2019, a lone gunman walked into 2 mosques within minutes of each other in Christchurch, New Zealand, and opened fire with semiautomatic weapons, killing 51 and wounding many more. We spoke to Greg Robertson, MB ChB, the surgeon who coordinated the medical response to this mass casualty event. Robertson talks about what his hospital had to do to manage all these casualties and also how New Zealand quickly changed its laws to restrict the availability of weapons used for these sorts of attacks.