In his note, Mr Batcha wrote that he blamed nobody for his death, but that he was embarrassed by "raids and media limelight over the 2G spectrum scam."
He also wrote that Mr Raja and his wife "are good people."
The Tamil Nadu government has transferred the death case of Mr Batcha to the Central Bureau of Investigation (CBI).
Mr Batcha, who was 47, had been interrogated twice in the last few weeks about the 2G spectrum scam, mainly because the company he headed was believed to be a front for the massive bribes that were allegedly paid to Mr Raja in return for the licences that he gave at baffling bargains to companies in 2008.
The CBI is investigating the scam, described as India's largest swindle.
Like Mr Raja, Mr Batcha was from Perambalur. He was the Managing Director of Green House, a real estate company which is owned and operated partially by Mr Raja's family. The former minister's brother is a primary investor and Mr Raja's wife serves as the firm's legal advisor.
Mr Batcha's wife, Bhanu, said that she last saw her husband at 10 am before his bath. Two hours later, when there was no sign of him, she asked her driver to help her break open the locked door.
There are conflicting reports on whether Mr Batcha was scheduled to fly to Delhi later today to meet with investigators. Sources in the CBI say he had been approached to turn approver in the 2G scam.
In Chennai, Opposition leader Jayalalithaa blamed Mr Raja's party, the DMK, for his death. She also said that Mr Raja should be provided with special security. "Otherwise he could also go the Sadiq Batcha way," she said in a press release.
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