Investors who are suing a group of traders and banks, saying they colluded to fix bond prices, have named four more banks as defendants. An amended copy of their lawsuit, filed in US District Court in Manhattan on Monday, shows BNP Paribas, HSBC, RBC and TD Bank have been added to the suit, which alleges that various banks and individuals manipulated the US dollar-denominated sovereign, supranational and agency (SSA) bond market.

Bond trader Gary McDonald, who worked at three of the banks, has also been named as a defendant in the amended lawsuit. The lawsuit alleges McDonald was also involved in colluding to fix bond prices.

They join Bank of America Merrill Lynch, Credit Agricole, Citi, Credit Suisse, Deutsche Bank and Nomura as defendants, along with individual defendants Hiren Gudka, Bhardeep Singh Heer, Amandeep Singh Manku and Shailen Pau, who have been named in previous lawsuits.

Bank of America, BNP Paribas, Deutsche Bank, HSBC and Nomura declined to comment. Credit Agricole, Credit Suisse, TD and RBC did not respond to requests for comment. Pau and Heer's lawyers declined to comment, while lawyers for Gudka and Manku did not immediately respond to requests for comment. McDonald could not immediately be reached for comment.

The amended lawsuit says lawyers for the investors have obtained transcripts of hundreds of electronic chats between the alleged conspirators, covering over 300 trading days. The suit says the alleged collusion began as early as 2005 and lasted for nearly a decade.

"This case concerns a brazen conspiracy to manipulate the market for US dollar denominated supranational, sovereign, and agency bonds," the lawsuit claims. "Rather than the dealer defendants competing with each other for the purchase and sale of SSA bonds to investors and to each other, the dealer defendants worked as one team."

In January last year, International Financing Review, a Thomson Reuters publication, reported sources saying that the US Department of Justice was investigating four London-based SSA traders and the banks that employed them for possible manipulation of bond prices.

Since then, several investors have filed complaints against the banks and individual traders allegedly involved. Monday's filing adds new details and allegations, including a sampling of chat transcripts, although some of the information, including the transcripts, has been redacted.

The redactions were necessary because of a confidentiality agreement associated with obtaining the documents, a person familiar with the matter said. The plaintiffs in the consolidated class action lawsuit include the Iron Workers Pension Plan of Western Pennsylvania, KBC Asset Management and Sheet Metal Workers Pension Plan of Northern California.

Copyright Reuters, 2017