I would have shrugged off Tommy...

So when Tommy tells Andy about Elmo Blatch...u gotta remember, Andy has very recently completed his tunnel at this point. Put yourself in Andy's shoes for a minute...

Sure, you would be wanting to clear your name...it's a big deal, I'm sure I'd want to do this. But 1) the Warden was unlikely to go along with this investigation and going around him would have proved difficult at best (even before an investigation started, the Warden took Tommy's life); and 2) even if you got an outside investigation started, you'd be in prison for another decade going through that and the appeals process. If the Warden was replaced, Andy's tunnel was certain to be found out about...attempted escape, another charge with a prison term.

Wouldn't it be easier...and better...to just stay with the tunnel plan? Heck, you've been digging for 20 years now, I'd hate not to use it right after I got done! Plus think of the money...you'd be unlikely to get much of a settlement back in the 50s...but after visiting a dozen banks in the Maine area after escape, you would have plenty of money to start your dream boat business. You'd much more easily prove the corruption at Shawshank and get the Warden and his deputies arrested doing what Andy eventually did. With the benefit of hindsight...You wouldn't have had to of spent a month in the hole (you'd have been on a beach instead). Your buddy Tommy would still be alive. The Warden and the guards would get their comeuppance. You'd actually use the tunnel you spent 20 years building. Ok, you wouldn't clear your name legally, but you're essentially rich and living a great life. To me, I'm sticking with the original plan even after Tommy's story.