A day after Japan's worst train accident in nearly 30 years, police began questioning bickering railway officials Wednesday to determine which of the two companies involved was to blame.

Forty-two people were killed and 450 others were injured Tuesday when a three-car special express from Kyoto with about 600 passengers aboard smashed head-on into a four-car local train near Minaguchi, Shiga prefecture, 200 miles southwest of Tokyo.Police said they were questioning officials of West Japan Railway Co. which ran the special express train to the region for a ceramics festival, and of the Shigaraki Highlands Railway, which operated the local train.

Investigators suspect that the local rail company was at fault for letting its train go onto the single-line track 10 minutes later than scheduled after a delay caused by a signal failure, Hiroshi Saiki, a spokesman for the Transport Ministry said. The delay put the local train in the path of the express train, he said.

The local train was to have left Shigaraki station at 10:14 a.m. and enter a small turnoff to wait while the express passed, but a signal light unexpectedly stayed red and the driver remained at the station. After 10 minutes, Shigaraki Railway workers decided manually to convert the signal to green, according to police.