The 66-year-old has been convicted of corruption along with three close aides, including live-in friend Sasikala Natarajan. Jayaraman was one of the employees who worked at Jayalalithaa's Poes Garden residence in Chennai during the period under investigation. He testified that along with another staffer named Ram Vijayan, he transported large sums of money regularly from the politician's home to banks where several firms owned by Sasikala and Jayalalithaa held accounts.
Jayaraman told the court that Sasikala would ask him to take bags of cash regularly to different banks.
His statement helped the prosecution prove that as Chief Minister, Jayalalithaa was trafficking in undeclared cash which was being collected through illicit deals. Jayalalithaa's lawyers had argued that the increase in her wealth - from Rs 2 crore in 1991 when she took office to more than Rs 50 crore when her term ended - was based on the legitimate business of different firms that she owned.
But Jayaraman's deposition shot holes through that argument while also tracing the undeclared money straight to the chief minister's own home.
In 1996, Jayalalithaa lost the election in Tamil Nadu; in 2001, her party the AIADMK returned to power. That's when Jayaraman turned hostile, claiming that he couldn't recall who gave him the cash that he ferried to banks.
But a string of bank deposit slips signed by both men established their initial claim - of large cash payments made into the accounts of Jayalalithaa and Sasikala's companies.
Jayaraman was subsequently cross-examined by the prosecution in 2011. This time, he didn't contradict what he had said in his first deposition.
S Murugesh, Assistant to the Special Prosecutor in the case against Jayalalithaa, told NDTV that bank employees confirmed in court that Jayaraman used to arrive to deposit vast amounts of cash into the accounts held by Jayalalithaa and her aides.
Jayaraman is inaccessible now. But his original testimony against his former boss helped place her in prison and led to her disqualification from office half-way through her term term as Chief Minister. Her appeal against her conviction and her request for bail will be heard on Tuesday.