The gunman responsible for the shooting deaths in Würenlingen in the canton of Aargau on May 9th was known to police, who had searched his home in April looking for weapons, without uncovering anything.

The killer, who took his own life, was one of hundreds of persons in the sights of Swiss police because they were thought to be “dangerous”, SonntagsBlick reported on Sunday.

In a bid to reduce the likelihood of more massacres occurring, police are currently monitoring 2,000 people with the potential to cause violence, the weekly said.

Multiple murder cases are isolated but have recurred periodically in Switzerland over the past 30 years.

In February 2013, a worker used a gun to kill four employees before dying from gun wounds himself at the Kronospan wood processing plant in Menznau in the canton of Lucerne.

Mass murderer Friedrich Leibacher in 2001 shot dead 14 members of the Zug cantonal parliament, injuring 18 others, before turning the gun on himself.

In 1984, Günther Tschanun, the city of Zurich’s chief building inspector, shot and killed four employees in his department before fleeing to France, where he was arrested three weeks later.

He was sentenced to 20 years in jail.

In all these cases, there were warning signs prior to the attacks, but authorities were unable to take action to prevent the killings, SonntagsBlick said.

Cantons have subsequently embarked on “threat management” programmes that aim to curb violence.

“In many acts of violence in the past, there were warning signs in advance that were undervalued or not taken seriously in the overall context,” Thomas Zuber, commander of the Solothurn cantonal police told SonntagsBlick.

 “We are trying by means of information and active measures to prevent acts of violence from people who show threatening behaviour.”

The canton of Solothurn currently has listed 74 people who pose a threat.

“There are people with whom the authorities or the police have to deal with over and over again,” Zuber is quoted as saying.

“The population expects police to not only educate people about violent crime but to prevent it,” Reinhard Brunner, head of crime prevention with the Zurich cantonal police force, told SonntagsBlick.

The force currently employs ten managers who are working on “threat” files in the canton were almost 300 people are regarded as potentially violent, the paper said.

On the police radar are troublemakers who threaten officials, men who beat their wives, people who are at loggerheads with their neighbours and other groups of individuals, including Islamists, according to the report.

If need be, police can seize weapons, and in high-risk cases place people into preventive detention before they commit a serious violent crime.

The sharing of information with municipalities and other authorities is considered key to combatting people with the potential for violence.

The cantons of Lucerne, Schwyz and Glarus are also in the process of setting up “threat” management systems.