Sorry to hear of this.
if high voltage distribution lines were involved, then it's worth remembering that given enough voltage, anything conducts. Living wood, concrete, a human, natural fibre rope, all conduct very well at moderate voltages. HV lines run at variously 6.6kv, 11 kv, 32 kv, and up to 440 kv.
A complete path to earth is needed to electrocute anyone, so assuming the trimmer made contact, the deceased would need to have been standing on, or contacting, either a metal ladder or part of a tree. Either is very possible since nonconductive fibreglass ladders are generally only used where specifically electrical work is taking place. Another possibility is that a branch he was working on contacted the power line.
Remember also that distribution lines are not usually insulated, they may have a weatherproofing coat that looks like insulation but it's not. It just keeps the rain out.
Do be careful around power lines ... electrocution is a very nasty way to go, even a weak shock can throw you off a ladder and get you that way. There are published guidelines for separation distances but two favourites come to mind: Get the utility company to isolate the line, or stay the hell away.
