Sylvia Wynanda Seegrist was born on July 31, 1960, in Crum Lynne, Pennsylvania. She had a troubled childhood. During her trial, her mother, Ruth, revealed that Sylvia's paternal grandfather had sexually abused her when she was just 8 years old. Ruth did not find out about this abuse until Sylvia was 13. During a conversation about the abuse, Sylvia expressed that she did not realize how serious it was.

At the age of 16, Sylvia was hospitalized for the first time. She was diagnosed with schizophrenia. Over the years, she was hospitalized about a dozen times. After each stay, doctors reported that she was no longer a risk to herself or others.

As a young adult, Sylvia tried to join the U.S. Army. However, she faced bullying from other recruits who thought she was a lesbian. They teased her and played pranks on her. Because of her unusual behavior, which included behaving strangely at a fitness club, she was discharged from the Army after only two months.

Sylvia often visited Springfield Mall and sometimes caused trouble for people there. She made unsettling comments about violent events, saying that some mass shootings were “good.” There was an incident at a K-Mart where employees refused to sell her a rifle because they were worried about her behavior. Eventually, she did manage to buy a Ruger 10/22 from another store.

On October 30, 1985, Sylvia Wynanda Seegrist drove to Springfield Mall in Pennsylvania with two Ruger 10/22 rifles. She first went shopping for Halloween items and then worked out at a fitness club. After that, she returned to the mall.

Once at the mall, she got out of her Datsun B-210, retrieved her weapons, and began firing. The first shot was aimed at a man about 30 yards away, but he was not hit. He recognized her car and flattened a tire to stop her from escaping. Seegrist then approached the entrance and fired at a woman using an ATM but missed her. She shot and killed two-year-old Recife Cosmen, who was there with his family.

Once inside the mall, Seegrist continued firing at random, hitting stores and people. Many shoppers ran when they heard the gunfire. Ernest Earl Trout, who didn’t hear the shooting, was killed in front of a store. Augusto Ferrara was the last of her victims. A local graduate student, John Laufer, managed to disarm her while she was trying to aim her gun at him. He then guided her to a nearby store until mall security arrived. When asked why she shot, her response was, "My family makes me nervous."

After the shooting, Seegrist was sent for evaluation and later stood trial. On March 6, 1986, she was declared competent to stand trial. The court found her guilty but insane, sentencing her to three consecutive life sentences for each victim and additional sentences for the wounded. She was first taken to Norristown State Hospital, then to the State Correctional Institution in Muncy, Pennsylvania.

Her actions led to discussions in Pennsylvania about how to better care for mentally ill individuals. After a shooting event years later, her mother called for changes in mental health laws. Seegrist had previously lied on paperwork to purchase the rifles, despite having a history of mental illness.

Sylvia Seegrist spent more than two years in a state hospital before moving to Muncy State Prison for women. She had regular visits from her mother and ex-husband but later cut off contact with her family. By the late 1990s, Seegrist's mental health declined, and she became increasingly paranoid. Her situation highlighted ongoing concerns about the treatment of mentally ill people and the need for appropriate interventions in such cases.