Gordon Beurskens, 51, claimed pensioners Jimmy and Nettie McQue had given him “unlimited” control of their bank accounts so they could keep their money “below the radar”.
He said the £77,580 he took from the two octogenarians was an ongoing “loan” which he intended to repay with interest.
But a jury at Livingston Sheriff Court yesterday returned a majority verdict finding him guilty of embezzlement.
Last night, friends of the family said Mrs McQue died in hospital on Wednesday, before the jury reached its verdict.
When the decision was read out in court, Beurskens looked visibly shaken and appeared to be holding back tears.
Shortly after his conviction, the former West Lothian councillor was served with a proceeds of crime demand from the Crown.
The offence was committed between 2006 and 2009.
Beurskens served as an “Action to Save St John’s Hospital” member of West Lothian Council but lost his seat in the 2012 local elections.
Sheriff Kevin Drummond called for background reports and told Beurskens he would be sentenced later. Bail was continued.
Neither of Beurskens’ victims gave evidence.
The jury in the seven-day trial was told that former ironmonger Mr McQue, who suffered from dementia, had died several years ago.
Mrs McQue aged 87, was in a care home after suffering a stroke, until her death on Wednesday.
Beurskens had denied using a third-party mandate signed by the couple to drain money from their accounts into his own.
He was earlier found not guilty of money laundering after the prosecution withdrew the charge, brought under the Proceeds of Crime Act 2002.
The jury heard evidence from Mrs McQue’s 2008 police statement that she trusted Beurskens so much she would “sign anything” he put in front of her.
She expressed surprise to police that an £8,000 ISA had been cashed in without her knowledge and the money transferred to Beurskens’ bank account.
She added: “I don’t know why he has got this. I certainly didn’t ask him to do this. As far as I was aware I still had an ISA.”
She also told detectives: “I’ve been asked if I would have allowed Gordon to use our money to live his own life and lifestyle and I would say definitely not. He was not to do this.
“He should have known that it was our money. Now that we have seen how many accounts we have or seem to have, I am concerned.
“I have been gullible. I think Gordon has taken advantage of us. I would have signed anything if Gordon had asked as I had trusted him.”
She added: “I did say to Gordon once about his nice new house and his new car. I told him, ‘My, you are doing well’. I really can’t believe all this.”
The jury heard that Beurskens and his partner Sadie McMillan used the couple’s money to run up a bill of £1,638.70 at the Ritz Hotel in London’s Piccadilly.