By Amanda Zamora, ProPublica

In our ever-expanding quest to Free the Files, ProPublica is teaming up with Huffington Post in Denver, Detroit, Miami and Washington, D.C. to unlock political spending in the final stretch of the 2012 presidential campaign.

So far, more than 400 volunteers have freed political ads filed at television stations in 33 swing markets by telling us what would otherwise remain buried: who actually bought the ads and how much they spent. The Federal Communications Commission began posting political ad contracts online in August, but the files aren’t searchable by market or political group, and television stations aren’t required to upload them in a standardized, machine-readable format.

With better access to these files, we’ve been able to uncover spending by dark money nonprofits (which don’t have to disclose their donors) in New Mexico and Ohio Senate contests. In the case of Ohio, the nonprofit told the IRS it wouldn’t spend money to influence elections, but later spent $1 million on ads attacking Sen. Sherrod Brown.

To free the files, volunteers are using this interactive tool to answer four key questions about each ad contract. So far, we’ve logged an estimated $207 million in ad buys across the country — including millions in these Huffington Post local markets.

Denver: As Barack Obama and Mitt Romney were squaring off in the first presidential debate, we were freeing more than $22 million in ad buys from the candidates, parties, super PACs and nonprofits in Denver. So far we show Obama spending at least $6.65 million on ads to Romney’s $1.1 million. Karl Rove’s American Crossroads super PAC is also spending big in Denver with $2.1 million in ads logged vs. $729 thousand spent by its nonprofit cousin, Crossroads GPS.

Washington, D.C.: The D.C.-Hagerstown market captures some of the political ads targeted voters in the neighboring battleground state of Virginia. So far, volunteers have unlocked $21.3 million in ads there, with $7.1 million in ad buys logged for Obama and $3.4 for Romney. The U.S. Chamber of Commerce has also been active in Washington, with $269,000 spent on ads targeted toward viewers of 60 Minutes and the Washington Redskins.

Detroit: We’ve logged $10.7 million in ads so far in Detroit, with hundreds of thousands bought by congressional candidates and the usual super PAC suspects -- but several smaller PACs are spending big to influence voters around state issues. The People Should Decide, for example, has spent more than $1 million on ads pushing the state to require a public vote before building any new bridges or tunnels to Canada.

Florida: Obama and Romney are in a dead heat in Florida, but we’ve got a long way to go freeing the files in key Florida markets. We’ve logged nearly $22.5 million in ad buys so far in Jacksonville, Orlando, Miami, Tampa and West Palm Beach. In Miami, we’ve logged $981,000 so far from Obama and $219,000 from Romney, with Restore Our Future (supporting Romney) spending another $149,000.

The more files we free, the more data we have about who is spending to influence your vote. To volunteer, log in at www.propublica.org/freethefiles and join the Free the Files group on Facebook.

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