David Black, from Tennessee, was involved in the inquiry into the Ben Johnson affair in the wake of the Canadian sprinter testing positive at the 1988 Seoul Olympics. He ruled out the likelihood of systematic cheating on Mr Christie's part.
He told the court in the second week of the former world champion's libel action against John McVicar that there was a "very low probability" that Mr Christie's clean drug-testing record could be accomplished on a false basis.
A private individual would not have the necessary resources available to cheat the system that way, Mr Black said.
He added that each negative test result further verified that an individual was not a user of any of the products which could be included in the testing process. "I firmly believe that the process is capable of identifying an anabolic steroid user over time if 100 tests are carried out," he stated.
Asked by Mr Christie's counsel, Patrick Moloney, QC, whether this meant that a consistent steroid user would be caught, Mr Black replied: "Ultimately I believe so."
Mr Christie, 38, of Twickenham, south-west London, who has now retired from competition, is suing Mr McVicar over claims that he cheated his way to the top by using banned performance-enhancing drugs.
Mr McVicar argues that his article, "How did Linford get this good?", which appeared in the now defunct satirical magazine, Spiked, in September 1995, is true.
The Olympic gold medallist has told the court that he had been tested more than 100 times and had only "nearly tested positive" once in 1988, and was subsequently cleared, when a tiny quantity of a substance that could be derived from the legal health supplement, ginseng, was detected.
The hearing was adjourned until today.Reuse content