The Witness (1983), Infocom's second interactive mystery, by Stu Galley.
As described on the box:
FEBRUARY 1938, LOS ANGELES. FDR's New Deal is finally rolling. Hitler's rolling, too; this time through Austria. But as Chief Detective for a quiet burgh on the outskirts of L.A., you've got other fish to fry.
One gilt-edged society dame is dead. And now it looks like some two-bit grifter is putting the screws to her multi-millionaire old man. Then you step in and the shakedown turns ugly. You're left with a stiff and a race against the clock to nail your suspect... unless you get nailed first!
Nobody said a sordid family affair like this was going to be a cinch. Everyone from the knock-out heiress to the poker-faced butler may end up in the slammer before it's over. Ahead of you is a Gordian knot of motives and alibis. And the only testimony you can trust is that of your own eyes -- because you are The WITNESS.