The 36-year-old unemployed killer was of Turkish origin, recently separated from his wife, and lived in the canton of Schwyz, where he had a record for assault and for making threats, the Blick newspaper reported online.
On Sunday at around 11.15am he killed his 59-year-old mother-in-law, his 57-year-old father-in-law and his 31-year-old brother-in-law in Würenlingen, a municipality in the canton of Aargau, cantonal police said.
He then shot a 45-year-old neighbour before killing himself in a tragedy that has shocked the country.
The gun he used was not licensed, police said.
A woman living nearby told Blick she heard five shots in quick succession before a moment of calm followed by at least three more shots.
Police searched the killer’s home for weapons on April 2nd but did not find anything, the newspaper said.
He and his wife, a supermarket cashier, had three children who were put for adoption after the pair separated, according to the daily.
The man had a reputation for threatening neighbours, neighbours contacted by Blick said.
“We were all afraid of him,” said one.
“He has threatened us repeatedly and yelled at us.”
An investigation into the case is continuing.