The boxes were examined by Frontline and ProPublica as part of an investigation into the growing influence on elections of dark money groups, tax-exempt organizations that can accept unlimited contributions and do not have to identify their donors. The documents offer a rare glimpse into the world of dark money, showing how Western Tradition Partnership appealed to donors, interacted with candidates and helped shape their election efforts.

Though WTP's spending has been at the state level, it's best-known nationally for bringing a lawsuit that successfully challenged Montana's ban on corporate spending in elections, extending the provisions of the U.S. Supreme Court's landmark Citizens United decision to all states.

The tax code allows nonprofits like WTP to engage in some political activity, but they are supposed to have social welfare as their primary purpose. As reported previously by ProPublica and Frontline, when WTP applied for recognition of its tax-exempt status, it told the IRS under penalty of perjury that it would not directly or indirectly attempt to influence elections -- even though it already had.

The group is now locked in an ongoing dispute with Montana authorities, who ruled inOctober 2010 that the nonprofit should have registered as a political committee and should have to disclose its donors. WTP sued. A hearing is set for March.

In the meantime, the group has changed its name to American Tradition Partnership, reflecting its larger ambitions. This month, it sent Montana voters a mailer in the form of a newspaper called the Montana Statesman that claimed to be the state's "largest & most trusted news source."

The front page accused the Democratic gubernatorial candidate of being soft on sex offenders.

Donny Ferguson, American Tradition Partnership's spokesman and executive director, did not specifically address the documents found in Colorado or allegations of coordination made against WTP.

"American Tradition Partnership always obeys every letter of every applicable law," he wrote in an emailed response to questions. "ATP does not, and never will, endorse candidates or urge voters to vote for or against candidates .... These false allegations are old hat."

On its website, the group says its primary purpose is issue advocacy and combating radical environmentalists, whom it sometimes calls "gang green." It describes itself as a grassroots group backed by a broad membership of small donors.

When asked about the documents found in Colorado, Jim Brown, a lawyer for the group, said he was unfamiliar with them.

After being shown some of the documents by Frontline, Brown, in a follow up email, said his review indicated that they appeared to belong to a company called Direct Mail. Direct Mail and Communications is a print shop in Livingston, Montana, run by a one-time key player in WTP and his wife.