The 39-year-old was shot in the town of Wohlen, at a residential block where he worked as a caretaker. His daughter, who suffered gunshot wounds in the attack, was taken to hospital but is not in critical condition, a police spokesman said.

A 40-year-old Swiss man who lived in the same block has been arrested for the shooting though the motive remains unknown. The case is being investigated by the Canton of Aargau police and the local prosecution service, who have opened an intentional homicide case. The suspect has been admitted to a forensic psychiatric ward, a spokesman for the Aargau prosecutor’s office told the Keystone-SDA news agency on Monday.

Local officers received information about the shooting at 10am on Sunday, Polish private broadcaster Radio Zet reported, citing a police statement. Officers who responded to the call found the man’s body at the scene.

Police spokesman Adrian Bieri said the man’s daughter witnessed his murder up close, Swiss website Blick reported.

A woman living at the same address told journalists there were never any disagreements in the building and she was unable to explain what had happened.

“Suddenly several shots rang out,” she said. “Then all you could hear were screams. It was terrible.”

The woman said the victim’s wife and son ran out of their apartment screaming, then the son ran into the street yelling that someone was killing his father.