Pennsylvania’s treasury department is accusing about a dozen large financial firms of working together to illegally inflate the price of bonds issued by Fannie Mae and Freddie Mac over seven years.

A federal court filing by Pennsylvania Treasurer Joe Torsella late Thursday cites what his office says is evidence from a “cooperating co-conspirator” in a U.S. Department of Justice investigation into price-fixing in the secondary market for bonds issued by government-controlled companies.

Evidence cited in the filing includes brief transcripts of what it says are online chats by traders from various financial institutions that are the largest dealers of the bonds.

In the discussions, the traders allegedly agreed to fix bond prices at artificially inflated prices, cheating Pennsylvania and other buyers of the bonds. The price-fixing began in 2009 and lasted through 2015, and violates federal anti-trust law, Torsella’s filing said.

An analysis shows that pricing patterns are consistent with such a price-fixing agreement, the filing said. The “economic fingerprints” of the conspiracy diminished after January 2016, when the cooperating co-conspirator discovered it, it said.

Torsella’s office said it is bound by a confidentiality agreement and could not reveal how it came to receive information from the cooperating co-conspirator. It would not say who the confidentiality agreement is with.

Named as defendants are Barclays, Bank of America/Merrill Lynch, Citigroup, Credit Suisse, Goldman Sachs, BNP Paribas, First Tennessee, TD Securities, Morgan Stanley, Nomura, JP Morgan, Cantor Fitzgerald, UBS and HSBC.

JP Morgan declined to comment while other financial institutions contacted by The Associated Press did not immediately respond Friday. Some asked for a copy of the lawsuit.

The bonds are a cornerstone for the investment portfolios of government and institutional investors, and Torsella’s office said it expects that a large number of governments, public agencies, pension funds and other public institutional investors are victims of the alleged conspiracy.

Thursday’s filing is part of an ongoing case in federal court in New York’s southern district being led by Torsella’s office.

Pennsylvania is seeking class action in the case, which has consolidated lawsuits by various government entities, labor unions and public pension systems, including the city of Baltimore.

It said Pennsylvania’s various agencies bought or sold $63 billion in so-called GSE bonds during the seven-year period. Torsella’s office is in the process of determining how much money state agencies lost because of the alleged price-fixing scheme, officials there said.

The Department of Justice hasn’t filed any criminal charges and the cooperating co-conspirator is not directly identified in Torsella’s court filing.

Torsella’s filing identifies Deutsche Bank Securities Inc. as a co-conspirator and one of various entities that participated in the violations, but that are not named as defendants. A Deutsche Bank spokesman declined comment Friday.

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