Four auto thieves were arrested and 21 bikes were recovered from them, police on Thursday. The four thieves, identified as Vivek, Prashant, Dilshad and Usman were arrested last night by Dankaur Police and recovered 21 bikes with spare parts from them. They used to steal bikes on demand from Haryana, Delhi, Ghaziabad, Bulandshahar, Noida and Greater Noida and would sell them after changing the parts.