DySP Ganapathy (51) was found hanging from a ceiling fan in a room at a lodge in Madikeri on July 7 last year.
Prior to this, he gave an interview to a local TV channel, saying the then Home Minister K J George and two senior police officers AM Prasad and Pranab Mohanty would be responsible "if anything happens to me."
Stating that according to forensic reports in the media, documents that were in the mobile phone and computer of Ganapathy have been destroyed, Yeddyurappa said "it is clear that somebody who is very powerful is behind this. In this background, this matter should be referred to the CBI."
Yeddyurappa demanded Siddaramaiah's resignation taking moral responsibility for "destruction of evidence" in connection with the case.
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He said George must resign from the cabinet or he should be dismissed from the ministry.
Seeking a thorough probe, Yeddyurappa said a BJP delegation will call on Union Home Minister Rajnath Singh on August 26 and apprise him of the need for a CBI inquiry into the issue.
"If our demands are not met, BJP will launch a state-wide agitation," he said.