State prosecutors have not provided information on the charges against the man identified only as S. but he is thought to be suspected of supporting and belonging to a terror organization, state broadcaster SRF reported on Wednesday.
Winterthur is considered a hotspot for radical Islam in Switzerland with at least five men from the city near Zurich having travelled to Iraq and Syria to fight for Isis, the broadcaster said. The arrest of S. is, however, the first time authorities have detained a suspected key figure in the city's Salafist scene.
S., a convert to Islam, has close links to the inner circle at Winterthur's An‘ Nur-Moschee and is a respected figure among those wishing to convert to radical Islam, according to a report for the SRF current affairs programme Rundschau.
Rundschau trailed the man for over a year in preparing its report.
The show's presenters said the man had links to Winterthur's MMA-Sunna-Gym run by Valdet Gashi who later travelled to fight to Syria along with at least two other members of the fitness centre.
S. is also thought to be linked to the German radical ‘Lies!' (Read!) group which distributes free copies of the Koran. He allegedly travelled with group leader Abou Nagie to Barcelona to visit a firm which prints the Koran.
He is currently being held in a regional prison.
Winterthur, in the canton of Zurich, announced in May it was launching a new service aimed at preventing radicalization. The centre, modelled on a similar institution in Zurich and established for a limited period until 2018, will provide a contact point for the public to report and discuss cases of extremism and violence
In 2015, a Swiss war correspondent told a local newspaper that an Isis cell was operating out of a mosque in Winterthur
Meanwhile teachers, social workers and youth workers in the city were among those given training to spot potential cases of radicalization in a series of workshops last year.
The Swiss Federal Intelligence Service said recently the number of would-be jihadists in the country had risen to 76 since 2001. The FIS is currently monitoring some 400 potential jihadists and a dozen people have been charged with terror-related offences.
More than 60 possible jihadists are currently facing prosecution, Swiss attorney general, Michael Lauber said in March.