This post has been updated.

On Friday, a gunman strapped on a helmet camera , loaded his car with weapons, drove to a mosque in Christchurch, New Zealand, and began shooting at anyone who came into his line of vision. The act of mass terror was broadcast live for the world to watch on social media.

Forty-nine people were killed and more than 40 others were wounded in the attack, which occurred at two different mosques in the city. A suspect, Brenton Harrison Tarrant, was charged with one count of murder, with more charges reportedly expected. Three other people were detained by the police, but one was released hours later.

A 17-minute video of a portion of the attack, which leapt across the internet faster than social media censors could remove it, is one of the most disturbing, high-definition records of a mass-casualty attack of the digital age — a grotesque first-person-shooter documentation of man’s capacity for inhumanity.

Videos of attacks are designed to amplify the terror, of course. But what makes this atrocity “an extraordinary and unprecedented act of violence,” as Prime Minister Jacinda Ardern described it, is the methodical nature with which it was conducted and how it was engineered for maximum virality.