For millions of teenagers and video game enthusiasts, Discord is an everyday virtual hangout where users communicate in private chats or in community forums. The social networking app, which began in 2015 for gamers, has grown into a platform boasting more than 200 million monthly users worldwide, 90 per cent of whom play video games. In recent years the platform has repeatedly surfaced at the centre of investigations involving murder, mass shootings, extremism and the exploitation of minors. On Wednesday a teenager who murdered his 45-year-old mother, Angela Shellis, with a hammer and recorded the attack on a Dictaphone was...