Police shot and wounded the suspect after he threatened to also shoot officers who arrived at the scene after the shooting in the village of Daillon on Wednesday evening, said interim cantonal police chief Robert Steiner. The gunman was then arrested.
Steiner said the suspect was using a military rifle that was once standard issue in the Swiss army during the first half of the 20th century.
"The shooter pointed his weapon at our colleagues, so they had to open fire to neutralize him, to avoid being injured themselves," police spokesman Jean-Marie Bornet told Swiss radio. He said the shooter lived in Daillon, and the motive for the shooting was not clear.
Prosecutor Catherine Seppey said the shooter -- who was not identified -- knew several of the victims, but "he was not known for making threats." He was unemployed and had been receiving psychiatric care since at least 2005, when he was first admitted to a psychiatric hospital, and was under the care of the cantonal agency that provides services and counseling to the disabled, she said.
Three of the victims, aged 32, 54 and 79, died at the scene, and the two injured men, aged 33 and 63, were taken to hospitals, Seppey said.
"We have no words to express ourselves after an event like this," Christophe Germanier, head of the Conthey district where the shooting occurred, told a news conference.
It wasn't immediately clear how the shooter obtained his weapons, but the rifle is popularly sold in military surplus markets.
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Guns are popular among the Swiss. There are at least 2.3 million weapons stashed among a population of less than 8 million people. Gun clubs are popular in rural parts of the country, with children as young as 10 taking part in shooting competitions.
The country's firearms laws are relaxed, but haven't led to a high gun homicide rate. They have, however, raised concern about a high incidence of firearms suicides.
All able-bodied Swiss men who are required to perform military duty often take their army-issued rifle home with them even after completing military service. In 2007, the government began requiring that nearly all of the ammo is kept at secure army depots.
In 2011, voters rejected a proposal to tighten the gun laws, siding with gun enthusiasts, sports shooters and supporters of Switzerland's citizen soldier tradition.
Press; By JOHN HEILPRIN]
Geir Moulson in Berlin
contributed to this report.
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