AP

LONDON (AP) — The manufacturers of the doping sample bottles supposedly tampered with by Russian intelligence agents have introduced a new design in the last month to try to stay one step ahead of cheating scientists.

World Anti-Doping Agency investigator Richard McLaren found that FSB agents tampered with samples during the 2014 Sochi Winter Olympics, leaving no sign of scratches or marks to untrained eyes.

Expert testimony in McLaren's latest report revealed how thin strips of medal could push up a ring around the bottle's neck, allowing the Russians to replace dirty samples with clean urine.

Berlinger, the Swiss company that makes the bottles, is working with law enforcement specialists in Europe to perfect designs that are harder to break into undetected. A new bottle went into circulation on Nov. 15 for doping testing, although Berlinger declined to outline the new safety measures.

"We work with forensic specialists from different nations," Berlinger spokesman Hans Klaus said during a visit to London. "We want to always stay a little bit ahead of those cheating but you cannot avoid a system like the Russians built up."