BERLIN, Sept 21 (Reuters) - German politicians expressed shock on Tuesday over the killing of a 20-year old petrol station worker after an argument about a face mask and said that coronavirus deniers who are willing to use violence will not be tolerated. The killing on Saturday evening in the western town of Idar-Oberstein has hit the national headlines as it is one of the only such cases linked to COVID-19 restrictions. Prosecutors have said that the petrol station cashier had asked a 49-year old man who wanted to buy beer to comply with the rules and put on a mask. The customer refused and left but returned later wearing a mask which he pulled down when he approached the cashier who again referred to the rules. "Then the perpetrator pulled a revolver and shot the cashier in the head from the front. The victim fell to the floor and was immediately dead," prosecutor Kai Fuhrmann told reporters. Flowers are placed in front of a gas station in Idar-Oberstein, Germany, September 21, 2021, after a 20-year-old gas station attendant who asked a customer to wear a face mask was shot dead last Saturday, September 18, 2021. REUTERS/Annkathrin Weiss Flowers are placed in front of a gas station in Idar-Oberstein, Germany, September 21, 2021, after a 20-year-old gas station attendant who asked a customer to wear a face mask was shot dead last Saturday, September 18, 2021. REUTERS/Annkathrin Weiss The suspect later gave himself up at a police station, saying the coronavirus measures were causing him stress, said Furhmann. He is being detained. The killing took place a week before a federal election in which the far-right AfD has tried to woo voters with an anti-lockdown and anti-vaccine campaign. The party, on around 11% in polls, harbours many coronavirus deniers. On Tuesday, politicians responded to messages circulating on social media from far-right groups and so-called "Querdenker" (lateral thinkers) who deny the coronavirus which showed sympathy towards the killer. "The hate and incitement coming from these people who can"t be taught divides our community and kills people. They have no place in our society," tweeted Foreign Minister Heiko Maas who said Querdenker were celebrating the killing. Justice Minister Christine Lambrecht said it was disgusting how the killing had been misused to fuel hatred. "The state must counter the radicalisation of coronavirus deniers who are willing to use violence with all possible means," she said.