In the shooting at the Gutenberg-Gymnasium 12 teachers, a secretary, two pupils and a policeman lost their lives. The killer then turned the gun on himself.
It was the first school shooting suffered by Germany. It forced the Bundesrepublik to take a closer look at various aspects of its education and gun laws, leading to important changes that are still felt today.
In 2002 a compulsory psychological test was brought in for anyone under 25 who wants to legally handle firearms.
The legal minimum age for those who want to join a shooting club was raised from 18 to 21. For hunters the minimum age was raised to 18 from 16.
After another school shooting in 2009 which claimed the lives of 15 innocent victims, gun control laws were further tightened. Authorities were given the power to search the properties of a gun owner to make sure the weapons were securely stored. The raids could take place without prior suspicion and even without the consent of the owner.
The Erfurt attack also led to a fundamental change in the approach to how police respond to gun sprees.
During the attack special forces moved from room to room in the school after witnesses reported a second gunman. The slowness of the operation meant that emergency services were not able to get to victims who needed treatment.
After the attack police introduced rules meaning that even a normal policeman should immediately enter the building and confront the gunman.
In Thuringia, where Erfurt is the state capital, 16 psychologists were engaged after the shooting to look after vulnerable students. By 2012 the state had employed 35 full time school psychologists.
Nonetheless, the Federal Association of psychologists says that in 2017 none of the 16 German states have enough specialist psychologists to care for school pupils - a number they reckon at one psychologist for every 1,500 students.
The shooting also led to an overhaul of how pupils qualify from Gymnasium (high school) in Thuringia.
The young gun man had been expelled from school shortly before sitting his Abitur (final exams), meaning that he was left with no qualification at the age of 19.
A new law brought in after the attack meant that all Gymnasium students would be awarded a qualification, even if they did not pass their Abitur. The qualification would allow them to apply for placements at vocational training colleges.
A further new regulation meant that it became compulsory for schools to inform parents of adult students if the student suddenly stopped performing well or were subject to a disciplinary proceeding. The shooter's parents had remained unaware that he had been expelled, after he repeatedly misled them about appointments they should have had with the school.