Kevin M. LaCroix of The D&O Diary weighs in on coverage of criminal investigations: D&O Insurance: Corporate Criminal Investigations. He references a December 2008 article by Patricia Bronte of Jenner & Block entitled D&O Coverage for Corporate Criminal Investigations (.pdf).
The main issue is how your policy defines “criminal conduct.” Some policies defines it with “commenced by the return of an indictment.” That definition leaves out a lost money spent trying to avoid (or avoiding) indictment and responding to an investigation.