I wonder if he had found her secret stash of money and had been dipping into it or stolen it completely. Then maybe Helen found out, threatened to go to police so he killed her to silence her? He might have secret debts or a gambling addiction, and if so maybe he needed more money so he accessed her bank account abroad and police pounced.
True, sometimes there is a surprising story emerges once LE investigate everything going on with the person going back a few years. They'll certainly look at his financial situation.
In Canada, a case like this would take almost 3 years to go to trial, I'm glad this will be tried fairly soon.