A criminal was gunned down Saturday and three others were arrested after an encounter between them and Special Task Force (STF) personnel in Gorakhpur, Uttar Pradesh, police said.STF officials said they acted on information provided to them. When they tried to arrest the gangsters, they opened fire on the STF team, police said. Gangster Vijay Harijan was killed in the firing, while three criminals - Monu, Dhanesh and Raju Yadav - were arrested, police said.