Robert Williams, 43, who buys and sells rare coins for his private collection, told Los Angeles authorities that a family friend visiting from Argentina did not understand that coins he had left in his office were collectible and hence exchanged them for three one dollar bills.

The coins included two 1969-S Lincoln Cents with a Doubled Die Obverse, each worth roughly $25,000. 

Williams said his entire family retraced the steps of their Argentinean visitor, including purchases made at a nearby supermarket and fast food restaurant, but were only able to recover four of the valuable quarters, dimes, nickels and pennies. 

The coin collector said all of the coins were insured against theft or damage, but it is still unclear whether spending them accidentally constitutes a recoverable loss. 

"Our friend is heartsick knowing that he purchased groceries and lunch that ended up costing us more than one-half million dollars," Williams said. "Truthfully, it was irresponsible of me to leave coins of such a high value out of their cases and in open view.  I blame only myself."

The Williams family spent six hours going through coin bags at the supermarket where their friend had shopped and did recover four of the missing coins.  "Searching for them was nasty and really was like searching for a needle in a haystack," he said.  "I'm surprised we recovered any."

Williams said he plans to post a full list of the missing coins and to offer a reward for any that turn up.  He acknowledged that the longer they stay in general circulation, the less likely they will turn up and the more likely their condition will be compromised.

"There is no telling where these coins might be by now," Williams said. "You probably have a better chance of winning the lottery than recovering one of these coins."