My instinct is to say that if – and it's a big if! – LW is certain the information is reliable, and that LW's friend doesn't already know, then LW ought to disclose it. Even thinking about the possibility of my loved ones believing I'd died by suicide when it was really an accident horrifies me!

I can definitely see an argument that LW shouldn't, that it's been so long that this information would just cause fresh grief. But LW says the friend is still actively struggling with trying to understand her brother's death, so it wouldn't be dredging up something she's not already thinking about.