A court in Poland has acquitted four men accused of murdering a former communist prime minister and his wife during a burglary six years ago.

The trial judge Cezary Pulawski said the police had made glaring errors during the investigation which effectively ruined any chance of collecting useful evidence.

The former prime minister, Piotr Jaroszewicz, who was in his eighties -- was strangled and his wife shot at their luxury villa near Warsaw in 1992.

At the time political motives were thought to be behind the the killings, but prosecutors said this was unlikely.