The owner of a peanut company blamed for a salmonella outbreak has appeared before a House subcommittee, but is refusing to testify.

Lawmakers ordered Peanut Corporation of America owner Stewart Parnell to appear at the hearing Wednesday. He showed up, but refused to answer questions, invoking his constitutional right not to incriminate himself.

After declining to answer lawmakers' questions, the committee excused Parnell and the company's Georgia plant manager Sammy Lightsey from the hearing. 

Earlier, the House Energy and Commerce Committee released the company's internal correspondence showing that Parnell was ordering tainted products to be sold even after confirmation of salmonella. Parnell complains in e-mails about losing money and says he's frustrated by the delay in shipping products.

Parnell was ordered by subpoena to appear before Congress on Wednesday to discuss the outbreak that has led to 600 illnesses, eight deaths and one of the largest recalls in history, more than 1,800 products pulled. His Georgia plant is blamed for the outbreak.

Rep. Greg Walden, R-Ore., revealed the internal correspondence from the company during a House Energy and Commerce hearing.

In prepared testimony, a laboratory owner told the House panel that the peanut company's disregard for tests identifying salmonella in its product is "virtually unheard of" in the nation's food industry and should prompt efforts to increase federal oversight of product safety.

Charles Deibel, president of Deibel Laboratories Inc., said his company was among those that tested Peanut Corp. of America's products and notified the Georgia plant that salmonella was found in some of its peanut stock. Peanut Corp. sold the products anyway, according to a Food and Drug Administration inspection report.

"It is not unusual for Deibel Labs or other food testing laboratories to find that samples clients submit do test positive for salmonella and other pathogens, nor is it unusual that clients request that samples be retested," Deibel said in prepared testimony to a House subcommittee. "What is virtually unheard of is for an entity to disregard those results and place potentially contaminated products into the stream of commerce."

Deibel said he hopes the crisis leads to a greater role for FDA in overseeing food safety and providing more guidance to food makers.

Lawmakers want to hear from Parnell, who was ordered by subpoena to appear Wednesday before the House Energy and Commerce's oversight subcommittee.

The investigation is starting to zero in on the question of who was responsible.

"Hopefully, people are going to be held accountable," said Rep. Bart Stupak, D-Mich., chairman of the committee's investigations panel.

Stupak says he wants know how Peanut Corp. managed to sell allegedly tainted goods month after month without triggering action by state and federal health authorities.

The company, now under FBI investigation, makes only about 1 percent of U.S. peanut products. But its ingredients are used by dozens of other food companies.

Federal law forbids producing or shipping foods under conditions that could harm consumers' health.

Peanut Corp.'s troubles mounted this week as the FBI raided corporate headquarters in Lynchburg, Va., as well as the Georgia plant. On Monday night, the company closed a second facility, in Plainview, Texas, after test results earlier in the day indicated salmonella was present in samples taken at the Texas plant. None of the products had been distributed to consumers, but the finding raised the prospect of a broader recall.

Further testing is needed to confirm the results, said Doug McBride, spokesman for the Texas Department of State Health Services.

After the results came back Monday, the FDA sent inspectors back to the Texas plant to check more thoroughly for signs of problems similar to those found at the Georgia plant, which has been identified as the source of the salmonella outbreak.

The company has said it is still investigating what happened and has expressed regret and concern for people who became ill. It is not clear whether Parnell will testify Wednesday or assert his constitutional right to not answer questions that may incriminate him.