A Connecticut state police officer outside a house in Newtown, Connecticut, a few days after the Sandy Hook killings last December. In carrying out the second deadliest school shooting in US history, 20-year-old Adam Lanza is said to have used 30-round magazines. Photograph: Joshua Lott/Reuters

The gunman who killed 20 children and six adults at a Connecticut elementary school last December fired 154 rounds in less than five minutes, s(...)