PRAGUE The A-4 sized envelopes are five centimeters thick and each weighs two kilograms. They're not unlike thousands of other items in the Czech post except that they are packed full of explosives.

At least eight of the letter bombs have been recovered in the Czech capital in the past nine days alone. These were all sent to executives of a property investment company that went bankrupt but citizens here are worried that they may also fall victim to one of the insidious devices.

"We're looking at every package very carefully and we painstakingly compare the address with a list given to us by the police," AFP quoted Karel Kettner as saying. The Czech Post Office board member is not to be envied these days.

"Of course people are worried that one of them is going to go off here too," said Kettner. "We're responsible for delivering the mail safely but also for the people who work here," said the official.

The wave of "terror", as Prague newspapers have been putting it, began last week. Four Prague-based businessmen received suspicious packages on the same say. Three of them immediately rang the police Pyrotechnical Department, who disarmed the devices. The son of one manager opened the parcel himself, losing several fingers when the device went off. Since then four parcels have been discovered in time and rendered harmless.

Police are tight-lipped about the letter bomb series. "We have five theories," said a spokesman this week. Investigations revolve around the former activities of the targeted managers -- all of them were members of the management of the H-System Property Investment Scheme.

The company set up in 1993 planned to build dozens of detached homes using money put up by 1,100 clients. Four years later H-System went bankrupt, leaving debts to the equivalent of around 50 million dollars and posing the question of whether embezzled are clients behind the letter bombs.

Eva Martinkova and Jitka Drunecka reject the theory. The two women are in charge of the "Svatopluk" and "Majak" umbrella organizations which look after the interests of 650 small investors. They believe the former managers may be settling old scores among themselves in true Mafia fashion.

The hoodwinked investors did strike back once before though and shortly after H-System went bust, one of its managers was on the receiving end of an arson attack.

The collapse of an investment company is not common in the Czech Republic but it does happen. Experts estimate that since the demise of communism small investors have been swindled to the tune of 1.65 million dollars.

Thousands of Czech have lost their savings in dubious business deals and banking failures and police do not rule out that the letter bomber may be just "somebody who was conned", a person who is hopping mad about what happened and who is not prepared to let the culprits evade justice.