When Brückner was about 10 years old his father was struck and killed by lightning, while he himself was left unconscious, an incident that was said to have caused a change of his character.
[4] Brückner had an interest in the supernatural and various books about witchcraft, ghosts, and evocation, as well as two Himmelsbriefe were found among his belongings when police searched his home.
in reference to Fritz Haarmann and Karl Denke, another serial killer whose crimes made headlines at that time.
He was believed to have killed his sister-in-law two years prior to the mass murder, and in the days leading up to June 6 he made various comments that indicated he had planned his crime for some time.
He waited for his brother-in-law, Hugo Birnstiel, and accompanied him for a while on his way, but eventually lured him into a forest, where he hit him with a piece of iron on the back of his head.
The 19-year-old managed to escape, whereupon Brückner returned to Lindenberg to the house of his parents-in-law where his estranged wife was living.
He waited for the pregnant woman at the outhouse and, apparently after she had declined his request to return to him, cut her throat with a knife.