Tower begins like it would have for anybody living in Austin on August 1, 1966: normal. We're introduced to the documentary subjects as they go about their day doing incredibly normal things: hanging out on the university campus, delivering papers, tossing rocks in the river. That normality only serves to make the audience queasy, though, because we know that it wasn't a normal day at all.

On August 1, 1966, a man climbed the tower at the University of Texas campus and opened fire on the people below. He killed 16 people and injured over 30 others in the 90 minutes of shooting. It was the first incident of a mass school shooting in the United States. Today we experience (far too often) "no, not again" tragedies but this was a "what is even happening" tragedy. It left the citizens of Austin traumatised; it left the whole of America traumatised.

Rather than approaching the attack like a history lesson with facts and infographics, Tower impressively transports us right to the day through reenactments and first-person testimonies from survivors and bystanders (read out by actors). These dramatised re-enactments are a mix of rotoscope animation and archival footage. The effect is slick, bold, and keeps all of the focus on the personal stories.

Tower's Artistic style is eyecatching

There’s a significant difference when hearing the stories told in the first person, as if it were still 1966. It makes it so much more immediate and emotional. It was like being right there, from the first shots ringing out to the numbing conclusion. To hear 18-year-old pregnant Claire Wilson recall the feeling of being shot and then lying on the hot pavement waiting to die is something that won't soon be forgotten.

There are also the stories of two police officers, other victims and bystanders, and a radio host who was on the scene. They describe the confusion and panic and fear in real time. Some hid, some helped, some became heroes and saved others. And throughout the entire retelling of the attacks—like a cruel soundtrack—gunshots ring out. It was difficult to listen so I can only imagine what it must've been like for the people who lived it for real.

Three-quarters through Tower, the story shifts and the animation blinks away and we see the subjects in the present day. The perspective shifts as they look back on that day and how far they've come since then. One of the bystanders talked about how that day separated the brave people from the ones who hid and she knew on that day that she was a coward.

This documentary is ultimately a human story and the shooter is only briefly mentioned by name. We aren't bombarded with the usual exhaustive investigation trying to find the "why." Tower reminds us that these tragedies are made up of people and their stories matter.

TOWER, directed by Keith Maitland, premiered on Friday 7 October at the 2016 BFI London Film Festival. Go here to learn more.