Peter Benstead, 72, of Crown Currency Exchange, was found dead in a car in a lay-by in Cornwall on 4 May last year.
The married father of three found the pressure of the trial "difficult to bear" and was "depressed and acutely confused" after suffering from a stroke, the inquest heard.
A conclusion of suicide was recorded.
Three others were jailed after the trial last year including Mr Benstead's son Julian, 46, who ran Crown Currency Exchange's sister company that specialised in trading cash for gold.
Julian Benstead was jailed for two and a half years for fraudulent trading while Mr Benstead's wife Susan was given a two-year suspended jail term for money laundering at Southwark Crown Court.
In a statement read to the inquest Mr Benstead's wife said he had disappeared from his home in Penzance one night. Police said he was found dead the next day in his car which was "full of overpowering fumes".
Mrs Benstead described how he left her a note written on kitchen towel in pink pen saying: "Sorry Susi but I love you. And this is the only way. Love you lots, Pete."
She said he had never talked about taking his own life.
The court case last year heard 12,500 people were left out of pocket when Crown Currency Exchange went under in October 2010. New clients' investments had been used to settle existing debts.
The judge said the evidence against Peter Benstead had been "overwhelming" but asked the jury not to return verdicts on the 10 counts of which he had been accused.
Mr Benstead's GP Dr Dan Rainbow told the inquest he had been on medication for stress but had refused offers of counselling. He said he had seemed "oddly relaxed" about the prospect of going to jail.
The boss of a currency trading firm killed himself while under "enormous stress" on trial for a £20m fraud, an inquest has heard.