The grisly slaying of a family of four in Tokyo's Setagaya Ward on Dec. 30, 2000, remains unsolved after a continuing probe involving thousands of investigators.

Mikio Miyazawa, 44, was found stabbed to death along with his wife, Yasuko, 41, their daughter, Niina, 8, and son, Rei, 6.

The Metropolitan Police Department has not made any significant progress, even though numerous apparent clues, including clothing believed worn by the killer, were found at the scene.

A senior official at the MDP's Seijo Police Station in charge of the investigation admitted police have yet to find a clue that could even point to a motive.

The MPD suspect the killings were carried out shortly before midnight by one young male, who apparently intentionally left his shirt and wool cap -- designed to resemble ones worn by a young popular actor in a TV drama aired at that time -- at the scene.

Evidence indicates the killer stayed in the house hours after the slayings, eating ice cream and operating Miyazawa's personal computer. He chopped up documents that belonged to the victim and dumped them in the bathtub, and used the lavatory, according to police.

The killer left a number of fingerprints -- stained with the victims' blood -- on the walls of the house.