Sorry for your loss, Al.
My father was a suicide, and there are two things you need to know:

You will never know what was in Dave's mind or the contributing issues that caused his action.  You will only cause yourself untold grief if you try to figure it out.

Try to stay out of the inevitable shit storm that will form around Scott & Tina.  I know this sounds callus (sp), but you were their employer as well as their friend, and you will be walking a tightrope on this until it all shakes out.  Try not to get splattered.

My apologies for the bluntness of my post, but this is the best advice I can give you. 

Be well, Hug your wife, Cry.