Any person or entity from Europe or any other part of the world may, in any language and anonymously or otherwise, report information to OLAF on serious misdemeanours relating to the performance of professional activities which have been committed by a member of the personnel of the EU or a member of a European institution if such information is liable to raise serious suspicions of fraud, corruption or any other illegal activity that may affect the financial interests of the Union.
You need not wait until you have proof - OLAF will conduct its own investigation.