“The SEC has done outstanding work in bringing cases built on the testimony of whistle-blowers,” said Matt Mittenthal, a spokesman for the attorney general’s office. “We look forward to continuing our productive partnership with the SEC to protect investors in the marketplace and root out financial misconduct wherever and whenever we see it.”

Schneiderman, 59, said he’s found an example of wrongdoing at Barclays based on information gleaned from former employees of Britain’s second-largest bank. His suit accused Barclays of trying to increase business at its dark pool by soliciting “predatory” high-frequency traders and then hiding their presence on the private-trading venue from other customers.

Active Investigation

One of several whistle-blowers involved in the investigation brought the allegations to Schneiderman after going to the SEC, according to one of the people, who like others who spoke to Bloomberg News asked not to be identified because the names of informants aren’t public.

SEC lawyers are actively investigating Barclays and have privately expressed frustration that Schneiderman, aided by fewer legal hurdles, brought a case so quickly, said a person with knowledge of the regulator’s examination.

To claim victory, Schneiderman still needs to successfully prosecute Barclays in New York court or settle with the bank. He could be in for a fight. The London-based bank asked a judge to dismiss the suit in July, saying it’s based on factual errors and fails to show any investors were harmed.

Mark Lane, a spokesman at Barclays in New York, declined to comment.

Other Cops

In the case of New York-based BlackRock, whistle-blowers went to the SEC in late 2010 to complain that an investment program relying on surveys of analysts gave the world’s largest money manager an edge in obtaining non-public information that could move stock prices, said one of the people. An SEC official eventually suggested that the informants consider sharing their concerns with other Wall Street cops, the person said.

The whistle-blowers did just that in July 2013 by going to Schneiderman. By January, BlackRock had agreed to end the surveys and pay $400,000 to cover the cost of his investigation. In settling, BlackRock said it’s committed to the “highest” ethical standards and that it discontinued the trading program to avoid even the appearance of impropriety.