SPOILER WARNING - Please read no farther unless you have already seen the movie.
Blake was Kathy's (Sandra Dee) boyfriend and was suspected of murdering Howard Mason due to a tape conversation but later was released. Does anyone know what cleared him? I think it had something to do with a phone call from Kathy.
Just watched this on DVD and found myself wondering the very same thing. You're right, it was never made clear. Then again, writers Ivan Goff and Ben Roberts were two impeccable craftsmen who would never have let a question like that go unanswered, so I'm sure an explanatory scene was shot and then later cut -- maybe for pacing?
Whatever the reason, it was a stupid decision, and that -- along with a rather lame ending that had (SPOILER) --
-- Anthony Quinn losing his footing and plummeting from the roof --
-- marred an otherwise taut and well constructed thriller.