The gunman shot three people dead and injured another six in the shooting at a wood-processing works last Wednesday.
Although the police have not confirmed how the shooter – identified as Viktor B. – died, reports had indicated that he had turned the gun on himself.
But the man’s family have cast doubt on the suicide theory, Blick said on Monday.
“Someone shot Viktor dead – from behind,” the paper quoted a cousin of the gunman as saying.
“We saw the body in Zurich on Friday before it was flown to Kosovo,” the relative said.
“The police said Viktor had not killed himself. He was hit in the back of the head. You can see where the bullet entered and came out,” the cousin said.
The father of three was buried in his home town of Nec in Kosovo on Sunday, Blick said.
Viktor B’s relatives are struggling to understand the motive for the crime but they believe the catalyst could have been a summons from his boss.
The gunman was said to have had problems at work and to have kept a distance from his colleagues.
He turned a pistol on co-workers during the morning break, killing a canteen worker and a Swiss wrestling champion. Another man later died in hospital.