Belle Gunness, originally named Brynhild Paulsdatter Størseth, was born on November 11, 1859, in Selbu, Norway. She was the youngest of eight children in a poor family and worked on neighboring farms from a young age. In 1881, she emigrated to the United States, settling in Chicago with her sister.

In Chicago, she changed her name to Belle and found work as a domestic servant and at a butcher's shop. She married Mads Ditlev Anton Sørensen in 1884. They opened a candy store, which later burned down, providing them with insurance money. Belle also collected insurance money from the deaths of two infants in her care, raising suspicions of foul play.

After her first husband's death in 1900, Belle moved to La Porte, Indiana, where she bought a pig farm with the insurance payout. She married Peter Gunness in 1902, but he died under mysterious circumstances eight months later. Belle continued to place marriage ads, luring men to her farm, many of whom disappeared without a trace.

Gunness's criminal activities were uncovered in 1908 when her farmhouse burned down, revealing multiple bodies buried on the property. Though Belle was presumed dead, the headless body found was never conclusively identified as hers.

In 1884, she married Mads Ditlev Anton Sørensen. The couple initially owned a candy store, which unfortunately burned down, as did their home. Both incidents resulted in insurance payouts to the couple.

Tragedy struck multiple times in Belle's household. Two of her babies died from inflammation of the large intestine—a condition that can result from poisoning—after which Belle collected significant insurance money, raising suspicions among neighbors who noted she never appeared visibly pregnant.

During 1900, on a day when two life insurance policies on her husband overlapped, Sørensen died of a cerebral hemorrhage, described by Belle as occurring after he had come home with a headache. She treated him with quinine powder, only to find him dead upon her return. This incident led to a payout of $5,000 from the life insurance policies, which Belle used to purchase a pig farm in La Porte, Indiana.

In 1902, Belle married Peter Gunness. Shortly after, while Peter was out, his infant daughter died under mysterious circumstances. Eight months later, Peter himself died from a skull injury caused, Belle claimed, by a falling meat grinder. The district coroner called a jury, suspecting foul play, but no charges were filed, and Belle collected another $3,000 in insurance money.

Belle's pattern of seeking companions through marriage ads began in 1905, attracting numerous men to her farm with promises of marriage. One respondent, Henry Gurholt, disappeared after moving to her farm, leading his family to unsuccessfully reach out to Belle for answers. Similar fates met other men, including John Moe, who vanished after withdrawing a large sum of money and visiting Belle.

The true extent of Belle's crimes came to light in April 1908 when her farmhouse burned down, revealing the bodies of a headless woman and her three children in the ruins. Further investigations uncovered the remains of at least 11 other people on her property.

The suspicions around Belle grew when Ray Lamphere, her hired hand and occasional lover, was arrested and later convicted of arson in connection to the farmhouse fire. He confessed that Belle had killed many of her suitors and suggested that she had staged her own death in the fire to escape detection. Despite these revelations and ongoing investigations, the full extent of Belle Gunness's crimes remains shrouded in mystery.