Sufficient evidence has been gathered during the pre-trial investigation that confirms the originality of the "secret ledger" of the Party of Regions, passed by former First Deputy Head of the Security Service of Ukraine (SBU) Viktor Trepak to the National Anti-Corruption Bureau of Ukraine (NABU).

According to the NABU press service, this is evidenced by the findings of a number of handwriting examinations, which confirm authenticity of the signatures of a number of individuals, as well as "numerous testimonies of people who personally made records and put signature in the "secret ledger" for receipt of cash."

As reported, in late May 2016 information provided by former First Deputy Head of the Security Service of Ukraine Viktor Trepak was promulgated. He said he had handed over to the NABU the documents confirming illegal payments of cash by the Party of Regions to a number of former and incumbent high-ranking officials. According to him, the matter concerns the so called "black books" of the Party of Regions with total payments of about $2 billion.