A spokesperson for G4S said the firm had not been provided with the results of the initial audit of the government electronic monitoring contracts with the government, despite requesting the report.
They said an internal investigation, with external help, found no dishonesty in the tagging contracts.
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According to local reports, the repairman had failed to disconnect the power to the escalator before getting to work.
Counter-terrorism forces, backed by Shi'ite militias on the ground and coalition airstrikes, are moving into the city on several fronts.