Stig Tommy Alexandersson was born on March 1, 1948, in Sweden. He grew up in the countryside outside Enköping, along with three brothers and three sisters. His family life was troubled. Alexandersson himself reported that his father was very violent. He mentioned that his father often controlled the family through fear and aggression. For example, his father would lift him up against a wall, hit him, and whip him with an inner tube.

In a shocking incident when Alexandersson was just five years old, he said that his father chased his mother with a large axe. This event forced her to climb out of a window to escape, wearing only her underwear. These experiences marked his early life with trauma and fear.

At the age of 14, Alexandersson decided to leave his home. After leaving, he turned to alcohol and drugs. By the time he was 20, he had gained a reputation in Enköping as a violent man who often drank excessively.

On 31 May 1988, Stig Tommy Alexandersson entered an apartment on Bjurholmsgatan in Södermalm, Stockholm. Inside were his former fiancée and a 53-year-old man. He attacked them with a clothes iron, hitting them in the head. He then used a knife-like object to slit their throats. After the murders, he placed the bodies in the beds, poured petrol over them, and set the apartment on fire. He was arrested but later released due to insufficient evidence.

On 22 September 1988, the same day he was acquitted for the earlier crime, Alexandersson went to the home of a couple in Tumba, just outside Stockholm. After some drinks, he argued with the man and killed him by slitting his throat. When the man's 74-year-old father came home, he was also killed with multiple stab wounds to the neck. A woman who visited them was killed with a cleaver. Alexandersson then poured denatured alcohol in the apartment and set it ablaze. The three bodies were found with their throats cut so severely that they were almost beheaded.

During the investigation, a witness saw Alexandersson, covered in blood, buying petrol nearby. His fingerprints were also found at the scene. Despite this evidence, he denied any wrongdoing. The court convicted him and sentenced him to life imprisonment for five murders and two counts of arson. His appeals were rejected, and the Supreme Court of Sweden decided not to review the case.

While in prison, Alexandersson did not have any visitations or phone calls. He applied for a fixed-term life sentence multiple times but was denied each time. He made headlines in 2014 when he applied for a conjugal visit and detailed what items he wanted during this visit. He also had disputes with the prison service regarding his personal belongings, including a pair of shoes he claimed were discarded.

As of 2025, Alexandersson remains in prison, continuing to serve his life sentence.