Prosecutors went over a slew of documents and computer files with federal agents on Friday, showing how complicated the $20 million embezzlement case is against two former Starkey Laboratories executives and two of their business associates in U.S. District Court in Minneapolis.

The government has charged former Starkey President Jerry Ruzicka; former human resources head Larry W. Miller; and former business associates W. Jeff Taylor and Larry T. Hagen with theft and fraud charges in connection with the alleged embezzlement over a 10-year period beginning in 2006.

The defendants have denied all charges, and their attorneys have said Starkey's owner, Bill Austin, either knew and approved of their actions, or gave the executives in question the authority to do certain functions without his permission.

Allegations in the case include the creation of sham companies, fake invoices, and secret payments of commissions, rebates and bonuses. The majority of the theft allegations, however, center on the transfer and sale of restricted stock in a Starkey subsidiary called Northland Hearing Centers.

Two other fired executives — former Chief Financial Officer Scott Nelson and former Northland President Jeff Longtain — have pleaded guilty in connection with the stock transfers and are both expected to testify in the trial.

On Friday, the third day of the trial, Federal Bureau of Investigation and Internal Revenue Service agents went over some of the evidence collected in the case, including an allegedly forged signature.

Assistant U.S. Attorney Surya Saxena and FBI special agent Brian Kinney showed jurors signatures on documents for Northland that were supposed to be Austin's. While both signatures were his name, they were markedly different. Kinney surmised the later signature was forged, allowing the defendants to later steal $15 million in restricted stock from Austin.

The first document Kinney showed jurors was an Austin signature from 2002, when Austin first set up a subsidiary called Northland U.S.

The second document showed a later "Austin" signature that was used to transfer a loan guarantee by Bill Austin from Starkey's Northland U.S. to a new entity called Northland Hearing Centers LLC, prosecutors said.

"This signature, in my investigation, does not resemble the signature of Bill Austin," ­Kinney testified at the trial in U.S. District Court before Judge John R. ­Tunheim.

He showed other Northland Hearing documents in which Ruzicka and Nelson were listed as top executives of the Northland Hearing subsidiary.

The government alleges that Austin never knew of and never approved the transfer of stock or loan guarantees from Starkey's Northland U.S. to Ruzicka, Nelson or Longtain.

Defense attorneys have long argued that Austin knew and approved the stock transfers, but was reneging on the deals after he found out Ruzicka was planning to start a rival hearing aid firm and recruit Starkey employees. Starkey officials have said in statements that those allegations are false and that the evidence will speak for itself.

Ruzicka's attorney, John Conard, however, leveled a discovery complaint against prosecutors on Friday. Conard told the judge that he had just learned that Nelson told prosecutors during interviews two weeks ago that Ernst & Young auditors allegedly discussed the Northland Hearing stock transfers with Austin in 2006. Conard complained that prosecutors didn't immediately disclose that critical information to the defense or the court until late Wednesday.

It should have been disclosed immediately after the interview, he said.

Such information would have potentially changed the opening statements for all four defendants, all of whom insist that Austin knew about Northland and other actions that the government has called ­fraudulent.

Tunheim said he would take the information under advisement before deciding if the prosecution had failed to observe a key rule in the discovery process.