AMAGASAKI, Japan - Rescuers pulled two survivors from the gnarled wreckage of Japan's worst train crash in decades today, and investigators raided the rail operator's offices for clues about why the train skidded off the tracks, killing at least 73 people.

Power shovels picked at the piles of twisted railway cars, peeling away layers of crushed metal to allow better access to the two train cars flattened against an apartment building that the train slammed into during Monday's deadly accident.

Police said an unknown number of bodies remained in the wreckage.

Agents swarmed eight offices of West Japan Railway Co., carting away cardboard boxes of documents. The probe into possible professional negligence has focused on the actions of the 23-year-old driver - who has not yet been accounted for - and the speed of the train.

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.

Victims' relatives struggled to comprehend their loss.

"I wish it were only a nightmare," Hiroko Kuki, whose son Tetsuji was killed in the crash, told public broadcaster NHK. "I only saw him the night before ... I wish he were alive somewhere."

The seven-car train that crashed Monday in Amagasaki was packed with 580 passengers when it jumped the tracks near this Osaka suburb and plunged into the first floor of an apartment complex. At least 456 people were injured.

Government inspectors hoped to recover a recorder with data on the train's speed and other details at the time of the accident, said Shimoda, a Transportation Ministry inspector who gave only his family name.

Monday's accident occurred at a curve after a straightaway. Passengers speculated that the driver may have been speeding to make up for lost time after overshooting the previous station.

The train had been nearly two minutes behind schedule, company officials said.

The driver - identified as Ryujiro Takami - 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.

They were investigating the case as possible professional negligence by the train operator, West Japan Railway, Co., a prefectural police spokesman said on condition of anonymity.