Who else has information for me?

Drop by Tuttle's house for any clues that might be left.

You should see all of the obvious people who had anything to do with Tuttle,
like the people he worked with.

Those are both the senior partners and the secretaries at his law firm.

See Sidney Sloane, Henry Swathmore, Whitney Cartwright('s wife), Margaret
Porter, Alice Spring, and Brenda Walker.

If I were you, I'd try to find Whitney Cartwright.

His wife told you to go to the Criterion Club.

Letters were sent to August Heathcliff.  Talk to him about those.

And visit Harold Diggs to see why he was passed up for that promotion.

Swathmore had an alibi, so you might want to check that out.