Lloyd Blankfein, the chief executive of Goldman Sachs, has hired one of America's top criminal defence lawyers to help him address claims that the bank misled clients in the run-up to the financial crisis, and Congress afterwards.

Shares in the Wall Street bank fell in late trading on Monday when it emerged that Blankfein had retained Reid Weingarten, criminal defence attorney at Steptoe & Johnson. Blankfein turned to Weingarten after the US Department of Justice began investigating the way Goldman sold subprime mortgage securities – the toxic investments that triggered the credit crunch.

Blankfein has also been accused of misleading a Senate committee – a claim that is emphatically denied by Goldman.

Goldman confirmed that both Blankfein and other senior executives at the bank had engaged their own lawyers earlier this year. The move was triggered by the Senate permanent subcommittee on investigations, which in April issued a damning report into Goldman's activities. This report was then passed on to the DoJ.

"As is common in such situations, Mr Blankfein and other individuals who were expected to be interviewed in connection with the justice department's inquiry into certain matters raised in the [Senate] report hired counsel at the outset," said a Goldman spokesman.

Weingarten specialises in white-collar criminal defence, and has previously represented former WorldCom chief executive Bernard Ebbers and former Enron accounting officer Richard Causey. Both men are currently incarcerated after being convicted of fraud charges.

Blankfein has not been charged with any offence. Goldman itself was charged in April 2010 with defrauding investors of more than $1bn (£606m), and later paid a $550m fine. In June, the bank was served with a subpoena by the Manhattan prosecutor.

The news that Blankfein had become a Weingarten client sent shares in Goldman falling by 4.7% to $104.25, their lowest level since April 2009.

Legal experts said the move would reinforce speculation that the legal fallout from the financial crisis is far from over.

"This was the last thing that Goldman Sachs or any institutions in the sector needed," Peter Kenny, managing director of Knight Capital, told Reuters.

Back in April 2010, Blankfein told the Senate permanent subcommittee on investigations that Goldman had behaved responsibly. He denied claims that Goldman had deliberately profited from the housing crash by betting that mortgage values would decline, while still selling mortgage-backed securities to other banks.

"We didn't have a massive short against the housing market, and we certainly did not bet against our clients," Blankfein said.

Senator Carl Levin, who chairs the subcommittee, subsequently wrote to the justice department and the Securities and Exchange Committee to ask them to probe Blankfein's statement. In May this year, Levin told reporters: "In my judgment, Goldman clearly misled their clients and they misled the Congress."

Goldman insists that the testimony given in April 2010 was truthful and accurate.