Rescuers untangling Japan's (search) worst train crash in decades uncovered body after body in the wreckage Wednesday to put the death toll at 91, but grim work remained in accounting for the dozens still missing, including the driver at the center of the investigation into the wreck.

A probe into possible negligence by operator West Japan Railway Co. (search) has focused on the actions of the 23-year-old driver, his lack of experience and suspicions that the train was speeding before it derailed and slammed into an apartment building on Monday.

At least 456 people were injured.

Rescuers at the crash site in Amagasaki (search), about 250 miles west of Tokyo, found at least 13 bodies in the early hours of Wednesday, Hyogo prefecture (state) police said. They also found a body seated at the front of the train and believed to be that of driver Ryujiro Taka, but that hadn't been confirmed, the Kyodo news agency said.

The death toll was expected to rise further, with police saying an unknown number of victims were still in the wreckage. Kyodo estimated that at least 52 people were missing.

Rescue workers used power shovels to peel away the twisted metal of the two worst-damaged train cars, flattened against the apartment building.

Investigators swarmed eight offices of West Japan Railway Co. on Tuesday, carting away cardboard boxes of documents in their probe into possible professional negligence.

Government investigators examining the accident site said they had found the train's "black box," a computer chip that stores information about the time and train's speed in the final seconds before an accident. But they cautioned that the contents would take some time to analyze.

National broadcaster NHK reported that police suspected the train was going 65 mph when it hit the curve where it derailed — well above the 43 mph speed limit.

Investigators said the driver may have been shaken after overrunning the last station by 130 feet and falling 90 seconds behind schedule.

Workers freed two survivors from the wreckage early Tuesday, and police said they did not expect to find anyone else alive.

The seven-car train was packed with 580 passengers when it jumped the tracks near this Osaka suburb and plunged into the first floor of an apartment complex. The accident occurred at a curve after a straightaway.

The driver got his train operator's license in May 2004. One month later, he overran a station and was issued a warning for his mistake, railway officials and police said.

Deadly train accidents are rare in Japan. Monday's accident was the worst rail disaster in nearly 42 years in this safety-conscious country, which is home to one of the world's most complex, efficient and heavily traveled rail networks.

A three-train crash in November 1963 killed 161 people in Tsurumi, outside Tokyo.

An accident killed 42 people in April 1991 in Shigaraki, western Japan.