The companies have been the focus of intense media coverage since the FDA said it believed 16 cats and dogs died around the country possibly from pet-food posioning.

Menu Foods said the U.S. Attorney's offices in Kansas and the western district of Missouri have targeted the company as part of misdemeanor investigations of whether it violated the Federal Food, Drug & Cosmetic Act.

Marc Ullman, a New York attorney for ChemNutra, described his client as a victim rather than an intentional violator of the law.

"As the facts exist today, I would be extremely hopeful that there were be no charges against any individual associated with ChemNutra," Ullman said.

He said the government also could file a complaint against the company itself, however.

"I really don't know where (the FDA) investigation is going to take them," Ullman said. "Unlike Menu Foods, I don't report my conversations with the U.S. Attorneys."

The five FDA officials, who arrived unannounced about 1:30 p.m. Thursday at the Summerlin office of ChemNutra, wore badges and were low-key, ChemNutra spokesman Steve Stern said. He said he was present during part of the search, as were ChemNutra Chief Executive Officer Stephen Miller and a receptionist.

"(FDA officials) were professional. They were polite. They were businesslike, even to the point of being engaging," Stern said.

The investigators stayed in the offices for about five hours.

"They were there to retrieve documents and image or mirror the (computer) hard drives," Stern said.

The search warrant specified documents dealing with wheat gluten, the material that ChemNutra is accusing of Chinese supplier of intentionally altering with the chemical melamine. The substance gives false high-content readings for protein, making the gluten more valuable. But melamine also may have harmed an undetermined number of pets around the country.

Stern said he issued a ChemNutra announcement on the FDA search at 9:29 p.m. Thursday and started getting calls at 2:30 a.m. from East Coast media representatives. He counted about 100 media calls since then.

"We have cooperated and complied fully with FDA investigators both prior to and since being served with today's search warrant and will continue to do so," Miller said in a statement.

Miller has not been charged with any offense but sale of adulterated food is a misdemeanor even if an individual making the sale is unaware of the adulteration.

Attempts to reach Menu Foods for comment failed, but the pet-food maker issued a statement.

"Menu Foods has been doing everything it can to cooperate with the FDA," CEO Paul Henderson said.

Menu Foods filed a lawsuit in Lyon County Court in Emporia, Kan., against ChemNutra earlier this week. The lawsuit accuses of ChemNutra of breach of contract and breach of implied warranties about the tainted wheat gluten. Menu Foods said it has been named as a defendant in more than 50 lawsuits.

ChemNutra spokesman Stern said Menu Foods was getting 120 tons monthly of wheat gluten from ChemNutra but was using 200 tons of the material. Menu Foods has not disclosed whether any of the other wheat gluten was adulterated, Stern said.

Ullman said ChemNutra was victimized first by its Chinese supplier of wheat gluten and by Menu Foods, which bought the imported material.

Ullman said some of Menu Foods' test animals died in early February after eating the pet food. Menu Foods learned that its pet food had been contaminated on Feb. 20, testimony before a Senate subcommittee shows.

Mark Wiens, chief financial officer of Menu Foods Income Fund, sold 14,000 units of the Toronto-based company on Feb. 26 and 27 at $89,681.

Yet, Menu Foods first informed ChemNutra to stop shipments of wheat gluten on March 6, according to ChemNutra. Two days later, Menu Foods told ChemNutra, "Oh, we think there may be a problem with the wheat gluten you sold us," Ullman said.

ChemNutra quarantined its supplies of wheat gluten the same day, Ullman said.

"This was a lot worse than it had to be because of Menu Foods' inaction," Ullman said.

Stern said ChemNutra continues to import and sell pet food materials to customers, but he said the FDA has stopped importation of wheat gluten.

The Associated Press contributed to this report.