Albertville secondary school is now deserted, save for the white boiler-suited police officers who can be seen examining empty classrooms.
They are looking for clues that will help them piece together the terrible events that unfolded here this morning.
It was around 0830 GMT that a 17-year-old former pupil, named locally as Tim Kretschmer, entered the school and started firing indiscriminately.
Police say he moved from room to room re-loading his weapon, shooting his victims in the head as he went.
Students leapt from windows of the school in a desperate bid to escape.
Nine pupils and three teachers, one of whom had only just joined the school, did not make it.
The gunman then made his escape in a car, shooting dead a passer-by as he did so.
In a town 40 km (25 miles) away he was cornered by police inside a car dealership.
A gun-fight ensued, two more passers-by were shot and killed and two policemen injured.
The 17-year-old gunman was also shot and killed but it is not yet clear whether it was by police or his own hand.
Back at the school, terrified parents were being reunited with their traumatised children.
The horror of a brutal assault in a quiet residential street in a small town in a relatively rural suburb of Stuttgart was sinking in.
The school, which should be full of vibrant, noisy children, is now empty.
Text-books and pens lie abandoned on desks, a solitary shoe is marked in chalk then collected in an evidence bag by a police officer.
Bicycles are left chained to the bike rack where children left them. How many of them will remain unclaimed?
This is not the first shooting in a German school.
In 2006, a masked man wearing explosives and brandishing rifles opened fire at a school in the western German town of Emsdetten, wounding 11 people before killing himself.
In 2002, a gunman killed 16 people and himself at a high school in Erfurt - the previous worst such attack in Germany.
Chancellor Angela Merkel says this is a time of grief for Germany, but inevitably there will be a fresh debate about firearms, school security and what led a young man to carry out such terrible and violent acts at his former school.