Investigators working for special counsel Robert Mueller likely got access to the National Rifle Association's tax filings and list of secret donors, McClatchy reports.

The newspaper group's Washington bureau attributed the speculation to legal experts.

Those experts maintain it would be routine for the investigators to secretly gain access to the NRA's tax returns from the Internal Revenue Service.

Prosecutors' requests to judges for access to tax information are usually made "entirely in the background with no notice to the subject of the investigation," said David Axelrod, an Ohio attorney, who had once prosecuted cases for the Justice Department's Tax Division.

And Michael Zeldin, a former senior Justice Department official, said "it would be basic blocking and tackling for the prosecutors to seek all relevant tax returns."

The NRA is required to identify so-called "dark money" donors on its tax forms. The organization's nonprofit status permits it to shield those donors' identities from the public, but not the IRS, McClatchy reported.

Those donors include companies and individuals who financed $21 million of the NRA's publicly disclosed pro-Trump spending, according to McClatchy.

Key to Mueller's NRA inquiry is whether Alexander Torshin, deputy governor of Russia's central bank and a close ally of Russian President Vladimir Putin, arranged for Russian money to go to the gun rights group to aid Trump, McClatchy reported.

The newspaper group noted it is against the law for foreign funds to be spent in an attempt to influence elections in the U.S.

Torshin has previously said he had shared a dinner table with Donald Trump Jr. at the National Rifle Association's annual convention in May.

And Spanish prosecutors have accused Torshin of money-laundering for the Russian mob. Torshin has denied the allegation.

McClatchy said it is unclear how the NRA became part of Mueller's ongoing Russia investigation.

Steve Hall, former chief of the CIA's Russia operations, suspects NRA leaders failed to realize the Kremlin saw their group as a tool for its "dangerous propaganda machine . . . That's the most innocent explanation: The NRA got snookered."