How to reset an iPhone 3GS with a password?

I found an iPhone 3GS that's locked with a passcode. How do I reset it? I have tried by holding the home button and then plugging it into my computer, but it doesn't work. I think a recent software update has changed the phone such that it can only be unlocked in a different way.

Added (1). I should add that I'm not interested in responses that advise me to return the phone. I can't find the original owner. The original owner hasn't even attempted to contact the phone. So just help me unlock it or don't bother to respond.

That's stealing. Return it to the owner. Also, you may want to check this out:

http://www.nypost.com/...KoRFfsrDJI

You may think it doesn't relate to you if you don't live in NY, but this is proof that the government takes stealing seriously (even iPhone's). If you would like a iPhone 3GS, they are free with contracts now from most carriers. Don't be a criminal.