NEW YORK (CNNMoney.com) -- The government charged an oil trading firm Thursday with manipulating oil prices, the first indictment to come down since the regulators began a new investigation into wrongdoings in the energy markets.

The Commodity Futures Trading Commission charged Optiver Holding, two of its subsidiaries, and three employees, with manipulation and attempted manipulation of crude oil, heating oil and gasoline futures on the New York Mercantile Exchange.

In May the CFTC announced a wide ranging probe into oil price manipulation. The agency says that there are currently dozens of investigations ongoing.

"Optiver traders amassed large trading positions, then conducted trades in such a way to bully and hammer the markets," CFTC Acting Chairman Walt Lukken said at a press conference. "These charges go to the heart of the CFTC's core mission of detecting and rooting out illegal manipulation of the markets."

The complaint filed Thursday names Optiver chief executive Bastiaan van Kempen, Christopher Dowson, a head trader of Optiver, and Randal Meijer, head of trading at an Optiver subsidiary.

The CFTC said the firm attempted to 'bang the close' by amassing large positions just before markets closed, forcing prices up, then selling them quickly, driving down prices and pocketing the difference.

The alleged manipulation was attempted 19 times on 11 days in March, 2007, the agency said. In at least five of those 19 times, traders succeeded in driving prices higher twice and lower three times.

CFTC stressed that the price changes were small and the manipulation isolated, and that the investigation has nothing to do with the recent heat the agency has taken on Capitol Hill over rising oil prices.

The CFTC is the government's main regulator of commodity markets. Lately its employees have been hauled before Congress and asked repeatedly whether manipulation or excessive speculation is playing a role in record oil prices.

Repeatedly, CFTC experts have said they have found no evidence that speculators - or investors who do not ultimately use crude oil - are to blame for the rising prices. They say trading information shows no correlation between investment activity and price swings.

Others, such as the International Energy Agency, have also said speculators are not to blame. They've pointed to other non-traded commodities that have risen in price even faster than oil, and to the fact that there is no evidence of a bubble, such as excess oil sitting around in storage.

Still, the correlation of a four-fold increase of investment money into oil futures and a four-fold increase in oil prices since 2004 has not gone unnoticed - and many lawmakers, consumer rights advocates and even some oil industry analysts say speculation is at least partly to blame.

Under that backdrop, the CFTC has been ordered to investigate the matter more thoroughly, dozens of investigations are underway. The agency may soon be given a bigger staff and wider powers under bills being debated in Congress.

Over the years, the CFTC has found isolated incidents of price manipulation - when an oil producer controls products to influence prices - or other cases of wrongdoing. Since 2002, the agency has charged 66 defendants with energy market violations.

In a recent case, BP settled a suit that alleged the company tried to corner the propane market to inflate prices in 2003 and 2004. BP agreed to pay a $303 million settlement.

But overall, most experts say the incidents are so scattered, and the energy market so large, that it's unlikely a single trader or group of traders can have substantial sway over prices.