(Bloomberg) -- Credit Suisse Group AG was sued by a pension fund that alleges the bank misled investors and let “high-risk clients” including Greensill Capital and Archegos Capital Management take on too much leverage, in one of the first lawsuits since the twin debacles.

The pension fund, City of St. Clair Shores Police & Fire Retirement System, filed the suit on Friday in federal court in Manhattan.

In it, the fund alleged that Credit Suisse had “concealed material defects in the company’s risk policies and proceduresand compliance oversight functions and efforts to allow high-risk clients to take on excessive leverage,” exposing the bank to “billions of dollars in losses.”

The meltdown at Archegos, the family office of investor Bill Hwang, unfolded as some of his biggest wagers started to move against him -- positions he’d built with significant amounts of borrowed money. Archegos relied on that leverage to supercharge its returns, setting Hwang up for the financial disaster that befell him and roiled the market.

Read More: God and Man Collide in Bill Hwang’s Dueling Lives on Wall Street

Archegos started out in 2013 with more than $200 million, a significant fortune but a modest sum in hedge fund terms. Within a decade, it had grown to some $20 billion, according to people who did business with Archegos, marking one of the fastest accumulations of private wealth in the history of modern finance.

Much of that stratospheric leap took place in the past year or two, as Hwang began to employ more and more leverage to boost his returns and as banks, eager for his lucrative trading business, obliged by extending him credit. Hwang, a name that few even on Wall Street had heard of until now, was suddenly worth more than Ray Dalio, Steve Cohen and David Tepper.

When the banks saw Hwang’s bets turn south, they required Archegos to put up more money to cover the decline. When it couldn’t, they began to liquidate his portfolio, which included Chinese technology companies and U.S. media giants such as ViacomCBS Inc. and Discovery Inc.

The rout has inflicted billions of dollars in losses on some of the banks, notably Credit Suisse and Nomura Holdings Inc. Others, including Goldman Sachs Group Inc. and Morgan Stanley, got out early.

(Updates with details of the lawsuit and context starting in third paragraph.)

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