Robert Steinhäuser was born on January 22, 1983, in Erfurt, Germany. He was a student at Gutenberg Gymnasium, a secondary school in his hometown. During his early school years, Robert performed well academically. However, by 1999, his grades began to decline.

In 1999, Steinhäuser dropped out of school just before taking his final exams. Concerned about his academic situation, his parents requested that he be allowed to repeat the 11th grade, which the principal approved. In October 2000, Robert joined a local gun club and received a gun license, which would become a significant detail later in his life.

In September 2001, Robert was absent from school for a few days. When he returned, he presented a medical certificate to explain his absence. However, this document was quickly discovered to be forged. Because of this, he was expelled from Gutenberg Gymnasium. At that time, the educational regulations in Thuringia meant that Robert had no qualifications after his expulsion, leaving him with limited job opportunities.

Steinhäuser did not inform his parents about his expulsion and pretended to continue going to school. On the day of a significant event in his life, he told his parents that he was going to school to take a math exam. This deception was part of a larger pattern in his behavior leading up to that day. Investigators later found that he had been searching the internet for information about the Columbine High School massacre and had related files on his computer.

On April 26, 2002, Robert Steinhäuser arrived at the Gutenberg-Gymnasium in Erfurt, Germany, armed with a 9mm Glock 17C pistol, a Mossberg 590 shotgun that he could not use, and a diving knife. He entered the school shortly before 10:58 AM without any disguise, carrying his weapons in a bag. Steinhäuser spoke briefly to the caretaker, inquiring about the school principal.

Afterward, he changed his clothes in a restroom, putting on a black face mask. At 10:58 AM, he opened fire in the school office, killing the deputy principal and secretary. When the principal heard the commotion and went to investigate, he had already exited the room. He then moved through the school, shooting teachers from the doorways of their classrooms.

At 11:05 AM, a janitor called the police, and the first police car arrived by 11:12 AM. During this time, Steinhäuser shot at the police, killing one officer. He encountered a teacher named Rainer Heise in front of an art room. Reports say he and Heise had a conversation after which Steinhäuser lowered his weapon. Heise pushed him into the art room, where Steinhäuser then shot himself.

The entire shooting spree lasted about 20 minutes. Steinhäuser killed 16 people in total, including ten teachers, two students, and a police officer, injuring one person. He fired around 71 shots during the event. His body was later found by a special police unit.