producing biological weapons. Because of the intense secrecy around biological weapons programs, it is challenging to assess the actual scope of biological activities and whether they are legitimate defensive programs or a violation of the Convention—except for a few cases with an abundance of evidence for offensive development of biological weapons. Soviet Union and Russia Despite being a party and depositary to the BWC, the Soviet Union has operated the world's largest, longest, and most sophisticated biological weapons program, which goes back to the 1920s under the Red Army. Around the time when the BWC negotiations were finalized, and the treaty was signed in the early 1970s, the Soviet Union significantly expanded its covert biological weapons program under the oversight of the "civilian" institution Biopreparat within the Soviet Ministry of Health. The Soviet program employed up to 65,000 people in several hundred facilities and successfully weaponized several pathogens, such as those responsible for smallpox, tularemia, bubonic plague, influenza, anthrax, glanders, and Marburg fever. The Soviet Union first drew much suspicion of violating its obligations under the BWC after an unusual anthrax outbreak in 1979 in the Soviet city of Sverdlovsk (formerly, and now again, Yekaterinburg) resulted in the deaths of approximately 65 to 100 people. The Soviet authorities blamed the outbreak on the consumption of contaminated meat and for years denied any connection between the incident and biological weapons research. However, investigations concluded that the outbreak was caused by an accident at a nearby military microbiology facility, resulting in the escape of an aerosol of anthrax pathogen. Supporting this finding, Russian President Boris Yeltsin later admitted that "our military developments were the cause". Western concerns about Soviet compliance with the BWC increased during the late 1980s and were supported by information provided by several defectors, including Vladimir Pasechnik and Ken Alibek. American President George H. W. Bush and British Prime Minister Margaret Thatcher therefore directly challenged President Gorbachev with the information. After the Soviet Union's dissolution, the United Kingdom, the United States, and Russia concluded the Trilateral Agreement on 14 September 1992, reaffirming their commitment to full compliance with the BWC and declaring that Russia had eliminated its inherited offensive biological weapons program. The agreement's objective was to uncover details about the Soviet's biological weapons program and to verify that all related activities had truly been terminated. David Kelly, a British expert on biological warfare and participant in the visits