Polish prosecutors said they would charge a signal controller for unintentionally causing a deadly head-on collision between two trains near the southern town of Szczekociny on Saturday.
At least 16 people were killed in the country's worst train accident in 20 years. A further 58 were injured, some seriously.
Prosecutor Tomasz Ozimek said the person charged over the disaster "directed a train to Krakow onto an incorrect railway track. That led to a head-on collision with a train to Warsaw."
Investigators, meanwhile, were still trying to determine whether the accident had been the result of human error. Transport Minister Slawomir Nowak said that the technical conditions of the tracks or of the trains were not under suspicion at this time.
President Bronislaw Komorowski ordered the period of national mourning on Monday. Flags were flown at half mast and all cultural and sporting events cancelled for two days.
Rescue workers continued to search the wreckage of mangled carriages to make sure that all of the dead had been recovered.
dfm/slk (Reuters, AP)