Shareholders and brokerage houses ditched Barclays at the end of last week, and who could blame them? In addition to its involvement in serial financial scandals — including the manipulation of interest rates and gold prices — the bank now stands accused of fraud related to its “dark pool,” essentially a private stock exchange.

Generally operated by banks, dark pools are supposed to be a safe way for institutional investors to execute block trades without worrying that their transactions will move market prices before the deal is completed.

A scathing lawsuit filed on Wednesday by the New York State attorney general, Eric Schneiderman, claims that Barclays repeatedly lied to brokers about the extent of aggressive and predatory high-speed trading in the pool — activity that exposed investors to precisely the type of price distortions they were trying to avoid and that, not incidentally, enriched Barclays by increasing the number of transactions executed in the pool.

The lying took the form of private and public assurances by Barclays that investors in its pool were continually shielded from high-speed trading when, to the contrary, the bank actively sought to attract such traders to its venue and even bolstered their trading strategies by giving them privileged information about the pool, according to the suit. All the while, the suit says, Barclays assured its clients that it sent their buy-and-sell orders to trading venues that offered the best terms when it actually sent almost all orders to its own dark pool first.