Busting an extortion module, the Amritsar city police arrested four persons while one of them was injured following a brief encounter near Company Bagh area. Those arrested included Simaratpal Singh and Amandeep Singh, both residents of Saidoke village in Mehta, Harpreet Singh alias Happy of Bhaini Miyan Khan village in Gurdaspur and Simarat Pal Singh of Rampura village.