Two jars of baby food purchased at the same store were contaminated with ground-up castor beans containing tiny amounts of the poison ricin (search).

Police said Wednesday they were looking for a man who may have witnessed the contamination of the jars, which also included notes that referred to an Irvine police officer.

U.S. Food and Drug Administration (searchofficials who tested the baby food said thehe purified form that can be deadly. Rather, it was a less toxic, natural component of the castor beans, which can be obtained from ornamental plants.

"It's unlikely there would be serious injury with the level of castor bean found in those two jars we tested," said Dr. David Acheson, chief medical officer with the FDA's Center for Food, Safety and Applied Nutrition (search).

Small amounts of the food were eaten, but the babies had no symptoms, he said. No arrests have been made.

Authorities called it an isolated case and said no more contamination was found at the store where the two jars were bought. "There's no reason to believe there is any more out there," said Dan Henson, a special agent with the FDA.

The jars of Gerber Banana Yogurt also contained notes that referred to an Irvine police officer whose name was not released, but their exact contents were not disclosed. The officer is not a suspect, authorities said.

Authorities have not disclosed a motive but want to question Charles Dewey Cage, 47, of Irvine, a possible witness who was "in the area at a relevant time," said Orange County District Attorney Tony Rackauckas.

On June 16, a man told Irvine police that as he prepared to feed his son, he found a note inside a jar of baby food warning that it had been contaminated. A similar case was reported by an Irvine couple on May 31 involving the same baby food, police said. A note was also found inside that jar.

The Gerber Products Co. (search), based in Parsippany, N.J., is working with investigators. Authorities told the company the contamination "absolutely" occurred after the food was manufactured, said Gerber spokeswoman Terry Boylan.

Gerber baby food jars are vacuum sealed and should pop when opened. Rackauckas said, however, that it is possible for a jar to make the popping sound even if it has been tampered with.

The district attorney advised people to buy jars with a plastic seal and suggested pouring the food into a plate to check it before serving.

Ricin can be fatal if swallowed, inhaled or injected. A dose about the size of the head of a pin could be enough to kill an adult, according to the Centers for Disease Control and Prevention.

The FBI still is trying to determine how ricin turned up in a U.S. Senate mailroom in February. The discovery led to the shutdown of three Senate office buildings for several days.

Also still unsolved are two letters found last year in postal facilities that contained vials of ricin and were signed by a mysterious "Fallen Angel," who objected to new government rules for longhaul truckers. One of those letters was addressed to the White House and was intercepted by the Secret Service.