Story highlights FBI says it would take a forklift to get the cash out of the container it's shipped in

Money arrived at JFK airport from Switzerland in a cargo container on Saturday

It's not clear when it was stolen, FBI says

Official says the money was headed for the Federal Reserve

The FBI is investigating the theft of $1.2 million from Swiss International Airlines Flight 17, which arrived at New York's JFK International Airport from Zurich, Switzerland, on Saturday afternoon, a spokesman said Tuesday. The money was in $100 bills, J. Peter Donald said, adding it's still unclear when it was stolen.

Flight 17 was a passenger flight with air cargo, including a shipment of currency, according to another FBI spokesman, Jim Margolin. After the plane landed, the shipment of cash was discovered to be $1.2 million short. Margolin said investigators have not determined whether the money was taken before the flight left Zurich.

He said the cash was missing from a container that the bank uses to transfer currency, which is loaded into a larger cargo container. He said it would take a forklift to lower the currrency container into the larger container, or to remove it.

A law enforcement official with knowledge of the investigation said the money was headed to the Federal Reserve. Andrea Priest, a spokeswoman for the Federal Reserve Bank of New York, had no comment.

Another law enforcement source told CNN the money belonged to a U.S. bank that was transferring currency from offices in Switzerland to the U.S. It was a transaction within the bank, but the money was passing through a Federal Reserve facility in New Jersey, according to the source, who said it's fairly common, when large sums are transferred, even internally, for them to go through a federal facility, where old bills are exchanged for new ones.

The shortfall was discovered Monday when the shipment was delivered to the Federal Reserve facility in Rutherford, New Jersey, the source said.

The Port Authority is declining comment, according to spokesman Steve Coleman.