FBI crime laboratory experts gave inaccurate testimony at the trials of defendants in the World Trade Center blast and the 1989 bombing of Avianca Flight 203 in Colombia, and lab scientists and technicians used shoddy analysis and did not follow procedures in scores of other cases, the Justice Department's inspector general concluded. Those findings, coupled with serious problems in the way lab officials conducted themselves in the Oklahoma City bombing and the O.J. Simpson case, are part of a sweeping, 18-month investigation into significant failures at the lab at FBI headquarters in Washington. In addition to conclusions about how lab officials have performed in court, the inspector general also found that the bureau's scientists and technicians did not properly document their test results and poorly prepared lab reports. Overall, in investigating work at the lab's three key sections - the chemistry-toxicology, explosives and materials analysis units - [Inspector General Michael] Bromwich said: "We found significant instances of testimonial errors, substandard analytical work and deficient practices." Investigators also discovered instances where dictation on lab reports was altered and lab supervisors did not properly manage their agents. Bromwich's report does not say when or why the problems began at the lab, but some of the cases studied date back to the 1980s. As early as 1991, top FBI management was alerted to failures at the lab.