Shapiro said such evidence would "appear to implicate individuals who have yet to be charged."
Other sources agreed, but declined to comment publicly.
The most recent trial ended in August, when a jury reached guilty verdicts against former UBS bankers Peter Ghavami, Michael Welty and Gary Heinz. Prosecutors said the men acted as both GIC brokers and providers, manipulating bidding on at least a dozen agreements to increase the number and profitability of the agreements awarded to UBS. They also submitted intentionally losing bids and arranged for UBS to receive kickbacks in exchange for manipulating bidding.
They are slated to be sentenced March 19.
In May, a jury reached guilty verdicts against Steven Goldberg, Peter Grimm and Dominick Carollo, former executives at GE Funding Capital Market Services Inc. Prosecutors said the men collaborated with brokers including CDR, IMAGE and UBS.
Evidence against them included testimony from cooperating witness Douglas Goldberg, a former CDR executive who said CDR gave "last looks" on bids to many firms, including GE, Financial Security Assurance Capital Management Services LLC, Bank of America, Société Générale, Lehman Brothers Inc., and JPMorgan and its Bear Stearns unit, according to media reports.
Steven Goldberg was fined $90,000 and sentenced to four years in prison. Carollo and Grimm were each fined $50,000 and sentenced to three years in prison. They are appealing the sentences.
U.S. attorneys also have requested that they pay a total of $6.9 million in restitution to muni issuers.
A number of other cooperating witnesses testified in the trials, including former CDR staffers Daniel "Dani" Moshe Naeh, Stewart "Zevi" Wolmark, Evan Zarefsky and Matthew Rothman, as well as Mark Zaino, a UBS banker, and Doug Campbell from Bank of America.
Others who pleaded guilty include CDR founder David Rubin, Brian Zwerner from Banc of America Securities LLC, JPMorgan bankers James Hertz and Alexander Wright, Martin Kanefsky, former chief executive of Kane Capital Strategies Inc., and Adrian Scott-Jones who worked at Tradition Inc., and Eurobrokers.
Sentencing hearings for many of them have been rescheduled multiple times.
As of Dec. 21, sentencing dates were Jan. 3 for Scott-Jones, March 15 for Campbell and Hertz, March 22 for Rubin, April 3 for Kanefsky and July 19 for Zwerner.
Sentencing dates for the others have not been set.
Court papers say the government has some 600,000 tapes, including recordings of executives at host of firms, including Sound Capital, IMAGE, Deutsche Bank Securities Inc., Bear Stearns, which was acquired by JPMorgan, and others.
The fact that the 13 cooperating witnesses have not yet been sentenced or that sentencing has been delayed leads some sources to think they are continuing to give prosecutors useful information that could lead to more indictments.
"That's par for the course. Sentencing is usually delayed for the reason that the government is pursuing other individuals," said Sabino. "You have no idea where this information is going to lead to."
Many of the large financial firms targeted by government investigators have already agreed to pay millions of dollars to settle related civil lawsuits.
In 2010 and 2011, five big banks or financial services companies settled charges with state agencies, state attorneys general and federal agencies, including the Justice Department, the SEC, the IRS, other bank regulators, according to the SEC.
GE Funding Capital Market Services Inc., settled for $70 million in December 2011. Wachovia, now Wells Fargo & Co., settled for $148 million in November 2011. JPMorgan Chase & Co., settled for $228 million in July 2001. UBS Financial Services Inc., settled for more than $160 million in May 2011. Banc of America Securities, now Bank of America Merrill Lynch, settled for $137 million in December 2010. That settlement did not involve the Justice Department because the bank received indemnity from criminal charges after offering to cooperate with the investigation.
Class action suits filed by issuers against many of the firms are still pending.
One was recently settled. On Dec. 14, a federal judge approved a settlement that calls for JPMorgan to pay $42.6 million and Wells Fargo to pay $35 million to a group of muni issuers including Baltimore, the University of Mississippi Medical Center, the University of Southern Mississippi, the University of Mississippi, the Mississippi Department of Transportation, the Central Bucks School District in Doylestown, Pa., and the Bucks County, Pa., Water and Sewer Authority.