John Charles Eichinger was born on February 18, 1972, in Malvern, Pennsylvania. He was one of four brothers in his family. Eichinger attended Upper Merion Area High School in King of Prussia. While in high school, he was part of a large group of friends who enjoyed playing Dungeons & Dragons. This gaming activity helped him meet Jennifer Still and Heather Greaves, who both caught his romantic interest during this time.

After graduating from high school, Eichinger got a job as a clerk at a local Acme supermarket. He worked alongside Heather Greaves, which allowed him to spend more time with her. In his free time, he also participated in local chess tournaments.

On July 6, 1999, John Eichinger went to Jennifer Still's home in Bridgeport. He had a knife hidden under his jacket and planned to confess his feelings for her. However, when Still rejected him, Eichinger became angry. He pulled out the knife and stabbed her multiple times before cutting her throat. After the murder, Eichinger tried to mislead police by claiming he was in New Jersey and that two other Dungeons & Dragons players might know something about the murder. However, DNA evidence later ruled out those individuals.

Eichinger kept the bloody knife, his clothes, and rubber gloves as trophies of the crime. Every Halloween for the next five years, he would wear a Ghostface mask and take the knife with him when he went trick-or-treating.

On March 25, 2005, Eichinger was tasked with delivering flowers to Heather Greaves, who lived in King of Prussia. He again had a knife with him. After confessing his feelings to her, he was rejected once more. In a fit of rage, he stabbed Greaves and then slit her throat. Greaves’ sister, Lisa, and her 3-year-old daughter, Avery, were present in the house during the attack. Eichinger killed Lisa when he went to the bathroom and then caught up to Avery in the hallway, killing her as well. A neighbor saw Eichinger leave with blood-stained clothes.

Police connected Eichinger to the murders when they learned that Still and Greaves were friends and both had a mutual connection with him. Detective Richard Nilsen questioned Eichinger at his workplace, where he initially made excuses for his injuries. However, under pressure, he confessed to all four murders. He was extradited to Pennsylvania and charged with four counts of capital murder.

During the trial, Eichinger's defense claimed he suffered from a mental disorder and was under emotional stress due to his father's death. The prosecution argued that he had planned the killings and murdered Lisa and Avery to eliminate witnesses. Eichinger was found guilty of all counts. He received three death sentences for the murders of Greaves and her family and a life sentence for Still's murder. Although he attempted to appeal his sentences, they were consistently denied.

In 2008, his death warrant was signed, yet the execution has not yet taken place. An execution notice was signed on January 9, 2023, with a date set for March 7, 2023, but that execution was also not carried out.