In what could be a politically explosive decision, prosecutors in Zambia have decided not to pursue a case against two Chinese supervisors who shot 13 coal miners last year during a wage protest, the managers’ lawyer said Monday. The episode, which occurred at the Chinese-owned Collum Coal Mine on Oct. 15, was viewed as an outrage by many Zambians who resent the enormous economic influence China has over their country. At the time, the government said the shootings, none of which were fatal, would be vigorously investigated. Prosecutors arrested the two Chinese supervisors — Xiao Lishan and Wu Jiuhua — and charged them with attempted murder, but many civic leaders predicted a whitewash.