Dutch police have identified some 300 ‘dangerous loners’ and are continuously monitoring 15 of them because they could pose a serious threat to the public, according to media reports on Friday.

The majority of them are confused, have psychotic problems or hear voices, police chief Henk van Zwam told the Volkskrant on Friday.

‘Police and mental health officials work closely together,’ said Van Zwam, who is in charge of the project. ‘The aim was to intervene and to see if we can offer help to limit the potential risks.’

Royal attack

Police began drawing up a list of potential lone wolf attackers after the Queen’s Day incident in Apeldoorn in 2009 and Remembrance Day disruption by a screaming man in 2010. In Apeldoorn, Karst Tates, a known loner, drove his car into the crowd watching the royal family motorcade, killing seven people.

According to Nos television, 15 of the potential lone wolves are considered so dangerous they under constant surveillance and are locked up in a police cell or institution on important days in the national calendar, such as Remembrance Day on May 5.

The lone wolves were identified by studying thousands of threatening emails and other threats made against royals, politicians, celebrities and other prominent people, Nos television said. This resulted in a list of 300 individuals, of whom 15 were considered capable of causing a serious incident.

The experiment had been due to expire but justice minister Ivo Opstelten will tell parliament on Friday he considers it so successful he plans to make it permanent.