A prosecutor says he plans to charge a traffic controller who was on duty when two trains collided head-on in Poland Saturday, killing 16 people.
The announcement Monday is the first indication that human error is the suspected cause of the crash, which happened when the trains ended up on the same track by mistake.
Prosecutor Tomasz Ozimek said an investigation so far indicates that the controller made a mistake while setting the mechanisms routing the trains.
Ozimek said the controller, who has not been identified, is to be charged with unintentionally causing a railroad accident. He hasn't been charged yet because he is in a state of shock and under doctors' care.
Another traffic controller has also been detained for questioning but has not been charged.