PEORIA — Federal officials seized documents and electronic records from three central Illinois Caterpillar Inc. facilities, including the global headquarters in downtown Peoria, Thursday morning as an apparent part of a criminal investigation into the company's tax strategy.

Agents from an alphabet soup of federal agencies lined up outside the main administration building, a data center in East Peoria and the logistics center in Morton.

"Caterpillar is cooperating," a brief statement from the company read.

The investigation appears to stem from revelations about the company's tax strategy as outlined in a 2009 federal wrongful termination lawsuit brought by Daniel Schlicksup. The lawsuit alleged the company shifted profits overseas and to offshore shell companies to avoid paying more than $2 billion in U.S. taxes. Schlicksup settled the suit in 2012.

Caterpillar, in its annual 10-K filing with the U.S. Securities and Exchange Commission last month, acknowledged a criminal investigation into the tax strategy. The company said in a statement Thursday afternoon that the search warrant related to that issue, "among other things."

Federal officials would not confirm the substance of the investigation.

In the February filing, the company included the following statement on legal proceedings in the filing: "On January 8, 2015, the Company received a grand jury subpoena from the U.S. District Court for the Central District of Illinois. The subpoena requests documents and information from the Company relating to, among other things, financial information concerning U.S. and non-U.S. Caterpillar subsidiaries (including undistributed profits of non-U.S. subsidiaries and the movement of cash among U.S. and non-U.S. subsidiaries)."

The statement continued: "The Company has received additional subpoenas relating to this investigation requesting additional documents and information relating to, among other things, the purchase and resale of replacement parts by Caterpillar Inc. and non-U.S. Caterpillar subsidiaries, dividend distributions of certain non-U.S. Caterpillar subsidiaries, and Caterpillar SARL and related structures."

'Swiss structure'

In his complaint against Caterpillar, Schlicksup alleged the company sold and shipped spare parts globally from its warehouse in Morton while attributing at least $5.6 billion of profits from those sales to a unit in Geneva, Switzerland. This scheme, which operated from 2000 to 2009, was known as the "Swiss structure." Caterpillar SARL is based in Geneva.

A different strategy, the "Bermuda structure," allegedly involved shell companies that had no business operations returning profits to the United States without paying taxes on them.

The company denied the allegations.

The accusations, however, prompted an inquiry by an investigative panel of the U.S. Senate. The probe found Caterpillar saved about $2.4 billion in taxes through the "Swiss structure" over the course of 13 years. The Internal Revenue Service eventually proposed a $1 billion tax increase and penalties for years 2007-2009.

The report said Caterpillar paid PricewaterhouseCoopers LLP $55 million to develop the tax strategy. Under the strategy, Caterpillar transferred the rights to profits from its parts business to a wholly controlled Swiss affiliate called CSARL, even though no employees or business activities were moved to Switzerland, the report said.

In exchange, CSARL paid a small royalty, and the income was taxed at a special rate of 4 to 6 percent that Caterpillar negotiated with the Swiss government, the report said.

Before the arrangement, 85 percent of the profits from the parts business were taxed in the U.S., the report said. Afterward, only 15 percent of the profits were taxed in the U.S. The rest was taxed at the special rate in Switzerland, the report said.

Shares of Caterpillar, which have risen 35 percent over the past year, went into steep decline just before noon as word of the raid on company headquarters and other facilities began to spread, falling almost 5 percent before recovering slightly to close at $94.36.

Workers sequestered

IRS agents were among the officials executing the search warrants on Thursday, and a copy of the search warrant obtained by the (Peoria) Journal Star indicated agents were seeking "documents regarding the movement of any products between the United States and Switzerland," among other items. A criminal complaint filed in federal court remains under seal.

At the downtown Caterpillar global headquarters building, at least some company employees were directed to the cafeteria and were told to remain there and not leave, according to one employee. Another source with direct knowledge indicated those sequestered included employees in the treasury, tax and accounting divisions, as well as from executive offices. At least some of those employees were released to go home for the day at approximately 11 a.m., with some being told that they would learn later in the day Thursday whether they'd be allowed to return to their offices on Friday.

An employee at Building AD in East Peoria said the arrival of agents at that facility was less disruptive than the one in downtown Peoria appeared to be, with agents executing warrants at the East Peoria site appearing to concentrate on securing emails and electronic records.

Some of the agents entering the headquarters building wore jackets bearing an Internal Revenue Service logo, while others appeared to be from the Federal Deposit Insurance Corp. Others simply denoted that they were federal agents. A placard in the window of one of the federal vehicles noted it was used by police from the U.S. Department of Commerce Bureau of Industry and Security Office of Export Enforcement.

U.S. Rep. Cheri Bustos, D-Moline, who represents the district that includes the Peoria and East Peoria sites searched, said she was "troubled" in a statement released by her office.

"I'm troubled by the events at Caterpillar today, but I am pleased to see they are cooperating with federal authorities," she said. "My first concern is for the thousands of hardworking men and women at Caterpillar who, for generations, have made Peoria proud by manufacturing the iconic, yellow Caterpillar Earth-moving equipment. I will continue to closely monitor this situation as it develops."

In January, Caterpillar announced it plans to move its global headquarters and about 300 top jobs to the Chicago area after decades in Peoria. Caterpillar also scrapped plans to build a new headquarters in downtown Peoria.

-- The Associated Press and GateHouse News Service's Laura Nightengale contributed to this report.