(Capcom's primary storyline)
The Great Lakes murders were a series of cannibalistic homicides perpetrated by people infected with the A-Virus against fellow citizens. The incidents were an accidental result of the dormant virus becoming active. These killings, which were concentrated around the Great Lakes, got the attention of the US government and BSAA shortly before the virus was deliberately activated in New York.
Following a failed drone strike by the CIA, former operative turned bio-weapons black marketeer Glenn Arias oversaw development of the A-Virus. This virus contained genes taken from the Plaga parasites donated by Los Iluminados. The virus thereby had more coordinated mental effects on the infected than the t-Virus, and certain individuals could be ignored entirely by infected. With the added benefit of the natural dormancy of the virus until being exposed to the 'trigger', Arias' network was able to infect tens of thousands via A-GUA brand mineral water without showing symptoms until the scheduled New York attack.
Despite Arias' plans, the A-Virus was known to sometimes mutate within a host and prematurely activate, turning them into Zombies. Murders soon took place in Michigan; Ohio; Wisconsin; Minnesota; New Jersey; Pennsylvania; New York and Ontario, in some cases by groups of Zombies.
Occurring over a period of four months in the leadup to Arias' attack, the US government was able to develop a vaccine.