As the FBI began investigating a failed Democratic congressional candidate tied to Republican Rep. David Rivera, the campaign amended its financial disclosures in an effort to clear up lingering questions about its book-keeping.

But instead, the revised disclosures — coupled with contradicting statements by Rivera who told a Miami blogger of some involvement in the Democrat’s campaign — raises more questions for a federal grand jury about the campaign of Justin Lamar Sternad.

At issue: payments to Expert Printing, a Doral company tied to Rivera that could have produced at least 135,000 mailers for Sternad’s campaign. Many of the mailers were sent out by a mail house paid in cash — sometimes in envelopes stuffed with crisp $100 bills.

Total cost to send the mailers out: Nearly $47,000.

Total cost to print the mailers: at least $33,000 and as much as $50,000, according to printers and political consultants from both parties not associated with the Sternad campaign.

Yet Sternad’s campaign finance reports only list a $6,000 expenditure to Expert Printing, the only printing company in his disclosures, which Sternad only acknowledged in his amended reports received by the Federal Election Commission on Aug. 21.

But the reports give no indication about how he actually afforded to pay for the mailers. What’s more, Expert Printing in turn paid $9,000 on behalf of Sternad to another vendor, Rapid Mail & Computer Services, to label the mailers and send them out, Sternad’s new reports show.

How and why Expert Printing paid Rapid Mail $3,000 more than it was paid by Sternad is unclear.

Enrique “Henry” Barrios, vice-president of Expert Printing, did not return calls or text messages for comment. Sternad won’t comment, as did his lawyer, Rick Yabor.

The FBI and Miami-Dade police launched a criminal investigation after The Herald first reported that the Sternad campaign had paid for the mailings in cash. The case is now before a federal grand jury.

Sternad’s campaign ended Aug. 14 when he lost the primary election against Democrat Joe Garcia, a Rivera rival who was savaged by a Sternad flier and who now faces Rivera in the general election in November.

Under federal campaign finance laws, it is illegal for federal candidates to knowingly and willfully file false paperwork. They also can only accept a maximum of $2,500 from contributors — including in-kind services such as complimentary printing or mail services.

“The point of campaign-finance laws is pretty simple,” said Ron Meyer, a campaign-finance expert and attorney in Tallahassee.

“The public has a right to know who’s giving what to a candidate for the sake of transparency,” Meyer said. “When the numbers don’t add up and when cash is involved, it raises a lot of red flags and legal questions.”

The FBI is now investigating the incident on behalf of a federal grand jury.

Rivera already faced a federal investigation for his involvement in a $500,000 secret payment from a dog-track that, along with other parimutuels, persuaded voters to allow Las Vegas-style slot machine gaming in Miami-Dade in 2008.

Rivera initially denied any involvement in or knowledge about Sternad’s campaign. But last week, Rivera told Miami-based blogger Nelson Horta that he knew his friend, Ana Alliegro, was working as a campaign manager for Sternad.