Despite a recession and rising unemployment, criminal cases investigated by Japanese police fell 4.7 per cent from a year earlier, marking the sixth straight annual decline, the National Police Agency said.

Of the 1.82 million cases, 75.5 per cent were intrusion or petty theft.

Felonies - murder, robbery, arson and rape - accounted for 0.5 per cent, it said.

But the number of random attacks - the murder or attempted murder of strangers - jumped to 14, leaving 11 people dead and another 32 injured. It was a jump from eight attacks in 2007 and four the year before.

In the most grisly incident, an auto factory worker in June killed seven people and injured 17 in Akihabara, a crowded Tokyo district which is the hub of comic-book and video-game subculture.

The attacker, Tomohiro Kato, swerved a two-tonne truck into pedestrians before going onto a stabbing spree.

The data was revealed a day after Japan was shocked by the slaying of a professor at Tokyo's Chuo University.

Mr Hajime Takakubo, a 45-year-old expert in integrated circuits, was stabbed 10 times in a campus bathroom. Police have yet to identify the attacker or the motive. -- AFP