An investigative panel of experts blamed Mizuho Bank officials' "lack of awareness" for the lender's failure to cut off loans its affiliate made to crime-syndicate members.

Hastily commissioned by Mizuho on Oct. 8, the panel of three external lawyers compiled a report spanning 102 pages, wrapping up a 20-day investigation that included hearings of 85 officials of Mizuho and its affiliate.

In...