De Ruyter made the comments in a submission to parliament's Standing Committee on Public Accounts (SCOPA), after giving an interview in February where he made sweeping corruption allegations against Eskom and South Africa's governing African National Congress party.
Shortly after the interview aired Eskom announced that de Ruyter would leave his job as CEO immediately, a month before he was due to leave his post in March.
On Wednesday de Ruyter said he could not corroborate or provide detail of certain allegations as he did not have documents and other material that remained with Eskom or law enforcement bodies.
He added that some of the sources through which he learned of alleged criminal and unlawful activities had legitimate fears for their safety.
ESKOM was also central to the "State Capture" allegations made about the administration of South Africa President Jacob Zuma, in which it was claimed that persons close to the president essentially looted state enterprises.
ANC Secretary-General Fikile Mbalula has rejected the corruption claims he levelled against the party and labelled him a failure as CEO.
The struggling utility is unable to supply enough power for South Africa which is currently experiencing the worst power cuts on record. Many households are without power for about 10 hours a day.
