Bill, that's awful and terribly sad. As Thistlintom said, I think the best you can do is to let them know that you care and that you're there for them if they need help with anything or a sympathetic ear. Give them space, but also check in with them once in awhile.
I'm going to quote a good friend who recently gave me this piece of wisdom (gained from personal experience):
The last thing I learned is how very quickly people move on and forget how much you’re still hurting. Weeks, months, years later, precious few even remember what happened and when. Which hurts a little but again, grief if so intensely personal and is so different for everyone. Unless you’re highly expressive about your feelings, people just don’t know where you are in the process.
Which is why I suggest doing the occasional check-in. Just knowing that you're still thinking about them can be a tremendous help.