In a letter to the New York Times yesterday, the bomber, who has been playing a deadly cat-and-mouse game with officials for 17 years, contradicted an earlier threat to blow up a plane leaving Los Angeles International Airport within the next six days. "Since the public has such a short memory,'' the letter said, "we decided to play one last prank to remind them of who we are. But we haven't tried to plant any bomb on an airline recently."
The authorities took the initial threat seriously and heightened security at the airport, causing delays of up to four hours for passengers just as the Fourth of July holiday rush was starting to build up.
The FBI confirmed that both letters were genuine and advised that all airmail shipments under 12oz should be held until they had been checked.
Postal officials estimated that this would ground 400,000 packages a day.
Many travellers due to leave from Los Angeles preferred to switch to nearby Burbank airport. In Sydney, Australia, a United Airlines flight from Los Angeles was evacuated after a device that turned out to be a broken clock-radio was found under a seat.
The advance communication from the bomber, whose last device killed a forestry industry executive in San Francisco in April, is unusual.
FBI psychologists are now suggesting he may be getting desperate, or even jealous of the attention given to the bombing of a federal building in Oklahoma City.
In the new letter, he expressed remorse for some of the injuries caused during his 17-year bombing spree. So far he has killed three people and injured 16. "We are not insensitive to the pain caused by our bombings," his letter says.