Romney's 2009 taxes stink:

he was actively running for president in 2007 and 2008. That means it's relatively unlike he was doing anything during those years that he thought couldn't withstand scrutiny. So why not release a nice even five years of tax data? Perhaps because of something that happened in 2009.
- Matthew Yglesias (link)

Further evidence comes from John McCain, who in 2008 reviewed 23 years of Romney's taxes. McCain has said"I can personally vouch for the fact that there was nothing in his tax returns that would in any way be disqualifying for him to be a candidate." And McCain did not review Romney's 2009 taxes.

There must be something absolutely damning in Mitt Romney's 2009 taxes, which "you people" will never see.

Mitt took the amnesty for illegally dodging taxes with his Swiss bank account.

EVIDENCE:

[Romney's financial] disclosure of his 2010 account omitted information about his Swiss bank account at the Union Bank of Switzerland (UBS). [snip] UBS was fined $760 million for putting Americans into abusive tax shelters and forced to reveal more than 4000 Americans who banked with them under numbered accounts.

The 4000+ Americans who were exposed by UBS were offered amnesty from criminal prosecution for tax evasion if they closed their Swiss Account, recalculated and paid all back taxes and paid a 25 percent penalty on the largest amount.

Romney closed his UBS account in the time required. He did not close his other foreign accounts.

The deadline to take the amnesty and pay the fines was in 2009, and it would show up on his 2009 tax returns.