KARACHI - Police arrested two killers involved in killing of 50 people, after an exchange of fire and recovered arms and hand grenades from their possession on Sunday.According to SSP district west Aamir Farooqi, the trade of fire between a police party and a band of five culprits took place in Maripur area. After the exchange of fire, law enforcers arrested two killers, while the three others managed to flee. A kalashnikov, a repeater, three hand grenades and bullets were seized from them.In the preliminary interrogation, the detained culprits, Waseem Pathan and Afzal belonging to Rashid Bengali group of Lyari, confessed to having murdered around 50 people.