From the BBC http://news.bbc.co.uk/1/hi/world/europe/4154748.stm Cypriot police have raided the offices of Helios Airways, a day after one of the airline's planes crashed in Greece, killing all 121 people on board. Officials said the police were looking for documents that could be useful in a possible future criminal investigation. Aviation experts and investigators are struggling to unravel the sequence of events which led to the crash. All but 11 of the victims were Cypriot and some 17 children are believed to have been among those who died. Security alert Officials said that all but six of the 121 victims of the crash may have been dead before the plane smashed into a mountainside in Greece. Helios said the company was co-operating fully with the police. "There has been no question of our failing to co-operate with the authorities at any time," it said in a statement. In Greece, three days of mourning have been declared for the island's worst accident in decades. Relatives of victims, who included 10 Greeks, have been arriving in Athens to identify the dead. Flight 522 had been heading for Athens en-route to Prague when it lost contact with air traffic controllers, sparking a security alert before it crashed on Sunday afternoon. Click here for a graphic showing what happened The pilot of the Boeing 737, 50-year-old German Marten Hans Jurgen, was among the dead. Experts looking into the cause of the crash believe a technical failure led either to a loss of cabin pressure or oxygen supply. Greek Interior Minister Prokopis Pavlopoulos said: "It seems the deceased, in most cases, although not all, expired before the crash." Coroner Philippos Koutsaftis told AFP news agency that the main hypothesis for cause of death was asphyxiation. However, a defence ministry source quoted by Reuters said it appeared that the bodies had been frozen solid. Greek police have arrested a man who claimed his cousin sent him a text message from the aircraft minutes before it crashed saying that everyone was frozen. Relatives have vented fury on Helios Airways, accusing the company of allowing an unsafe aircraft to take to the skies - a charge the Cypriot carrier denies. It has also denied a number of reports that it has grounded its entire fleet following the incident. Company chairman Andreas Drakou said the crash was a terrible tragedy and apologised for the delay in announcing the names on the passenger list. Both flight recorders have been recovered from the crash site but one of them is in a "very bad state", chief investigator Akrivos Tsolakis said. 'Out of control' Crews of Greek F-16 fighter jets which were scrambled after contact with the airliner was lost, reported seeing the co-pilot slumped in the cabin. They later saw two unidentified people trying to take control of the plane and could see oxygen masks hanging down in the cabin. "There had to have been a fast and brutal problem to cause the death of the pilots in the cockpit." Helios insists its plane was airworthy but Greek television has reported that the airline's fleet has had a history of technical faults. On one recent flight from Warsaw to Larnaca, it said, passengers were taken off the plane suffering from respiratory problems.