The disclosure was made by the FBI as part of its effort to block the release of a 40-page internal report dissecting its handling of the Kimball case.
Various officials have said publicly in recent years that they believed Kimball could have other victims, but the disclosure is the first confirmation that investigators are looking at specific cases.
The status of the ongoing investigations was outlined by Boulder District Attorney Stan Garnett when he denied The Post access to the 40-page memorandum described as an "FBI Human Source Validation Report." The Post has sought the document, which Garnett's office obtained during the successful prosecution of Kimball for four killings, under Colorado open-records laws.
The FBI objected to the release, convincing Garnett that making it public could imperil ongoing investigations.
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(Copyright 2010 The Denver Post)