Andrew John Engeldinger was born on January 27, 1976, and raised in Richfield, Minnesota. He graduated from the Academy of Holy Angels, a private Catholic high school. In 2000, he began working at Accent Signage Systems, a sign-making company in Minneapolis, where he remained employed for approximately 12 years. Colleagues described Engeldinger as a loner who often isolated himself, choosing not to engage in conversations or social activities with others. He reportedly ate lunch alone and avoided interactions during breaks.

Engeldinger's family noted that he had been exhibiting signs of mental illness for several years, including paranoia and delusional thinking. Despite their efforts to encourage him to seek treatment, he resisted and eventually became estranged from his relatives. In 2010, his parents enrolled in a 12-week class for families of individuals with mental illness, hoping to better understand and assist their son. However, their attempts to reconnect and support him were unsuccessful. Engeldinger legally purchased two Glock 9mm handguns and practiced shooting at a local range. A search of his home after the incident revealed packaging for 10,000 rounds of ammunition, indicating he had been stockpiling weapons and preparing for violence.

On September 27, 2012, at approximately 4:30 p.m., Engeldinger was called into a meeting at Accent Signage Systems to discuss his termination due to chronic tardiness and poor performance. Before attending the meeting, he went to his car and retrieved a Glock 19 9mm pistol, which he concealed in a holster. During the meeting with operations director John Souter and top manager Rami Cooks, Engeldinger was informed of his dismissal. He responded by saying, "Oh, really?" and then drew his weapon. A struggle ensued, during which Souter was severely wounded, and Cooks was fatally shot.

Engeldinger then left the office and encountered company founder Reuven Rahamim, whom he shot and killed. Continuing through the building, he entered a sign-display area and killed employee Jacob Beneke. In the loading dock area, he shot and killed Ronald Edberg, another employee, and Keith Basinski, a UPS driver making a delivery. Engeldinger proceeded to the production floor, where he fatally wounded production manager Eric Rivers and grazed another employee. The entire shooting spree lasted approximately five minutes.

Police received the first 911 call at 4:35 p.m. Upon arrival, officers entered the building and began evacuating employees and searching for the shooter. Engeldinger was found dead in the building's basement from a self-inflicted gunshot wound. In total, six people were killed, including Engeldinger, and three others were injured. The incident is considered the deadliest workplace shooting in Minnesota's history.