Five former laboratory technicians have been arrested by ICAC officers for allegedly forging test reports in relation to concrete used for Housing Department construction projects in Tin Shui Wai. The Independent Commission Against Corruption said last night that those arrested, aged 25 to 45, were released on bail pending further inquiries. The investigation originated from a complaint alleging that an employee of a laboratory appointed by the Housing Department obtained the help of department staff in getting prior warnings of site inspections. Inquiries revealed a scheme engineered by some staff members of the laboratory to submit false concrete test reports to deceive their employer and the Housing Department. So far there is no evidence to show any corrupt involvement of government employees, the ICAC said yesterday. The five were arrested on Monday during an operation codenamed Rainbow. The ICAC said they were previously employed by the laboratory engaged by the Housing Department to conduct tests on samples of concrete used by the Housing Department contractor at the sites to ensure the concrete met the required standards. The test reports were first submitted to the contractor before being forwarded to the Housing Department. It is alleged that between the end of 1999 and June 2000, the five fabricated reports in relation to about 13 tests. In June 2000, when the Housing Department conducted surprise inspections at the sites, it discovered that the laboratory's staff had failed to test two deliveries of concrete, the ICAC said.