(Covers information from the S.D. Perry novels)
Dees was the last person to contact White Umbrella from inside the facility complex, where he informed them that he had the components of a puzzle-lock placed around the mansion to prevent investigators from exposure from the more dangerous subjects (paranoid delusions leading to the creation of bizarre traps was a symptom of t-Virus). While Umbrella offered their assistance, they did not investigate for six weeks, and only then through Albert Wesker and his S.T.A.R.S. team.