The deadline for presenting the preliminary report to prosecutors was shifted twice because of the massive nature of the inquiry.
Police first began the investigation at their own initiative into possible criminal charges against the company. Following a major leak from a gypsum waste pond at the company's mine site in November 2012, police also began investigating complaints brought by the Kainuu Centre for Economic Development, Transport and the Environment and several environmental protection groups.
Prosecutors will now decide if formal charges will brought, or may order further investigations before making a final decision.
