Carl Doser

The criminal investigation department followed many leads and systematically searched for owners of Winchester rifles. However, there was little hope of finding the culprit until the fall of 1996, when a Winchester rifle was found hidden in the walls of a kitchen of a house belonging to a woman named Doser. The gun, which belonged to Carl Doser, was an Italian Winchester imitation with a short barrel. It was identified as the weapon used to kill the victims.

It was discovered that Carl Doser was a loner living in Basel. He had legally bought the rifle in 1973 from Hofmann & Reinhart Waffen AG. He had earlier been interviewed by the police, but he lied, telling them he had sold the gun on the flea market. However, Doser was not charged because a clear motive for killing the victims could not be found, with no recorded meeting between Doser and the victims. However, the majority of the Swiss population still believe Doser was the killer^{[citation needed]}.

Adolf "Johnny" Siegrist

A man named Hans Blaser felt that his business acquaintance Adolf "Johnny" Siegrist, who was related to the murdered couple, was the main culprit, with Doser assisting in the murder. Blaser, a combat shooter, claimed that Johnny had asked Blaser for a machine pistol.

The ammunition was bought three weeks before the crime, from R. Mayer AG at the Basler Steinenvorstadt, and was likely to have been bought by Johnny. The shop assistant at R. Mayer AG recalled that the man who bought the ammunition had asked for two packages of Kal. 38 Spez ammunition, with each package containing 50 rounds. The customer had asked for ammunition with extra heavy lead bullets, and had asked if the rounds would fit in his Italian Winchester rifles. He had mentioned that he was obtaining the ammunition for someone else.

Johnny was described as being occasionally irascible, and styropore heads that had been shot through were discovered in his flat. It is suspected that his motive for killing the victims was related to his relationship with the victims. In addition, Johnny, who was 1.5m tall and had a voice that sounded like a woman's voice, had an inferiority complex which could have played a part in his motive for killing the victims. It was also suspected that he wanted revenge against the Siegrist-Säckinger couple for having nicknamed him "Dölfeli", which is a belittling name for "Adolf", and "Globi", which is the name of a Swiss children's book's protagonist. He was arrested temporarily, but died in the mid-1980s.