Mexico City prosecutors say a 42-year-old man who pushed a woman onto the subway tracks in front of an oncoming train suffers from schizophrenia and is unfit to testify.

Witnesses signaled for the train to stop, but the conductor was unable to brake in time. The 62-year-old victim was hit by the train and died.

The city prosecutors' office said Tuesday that the man had been sent to psychiatric units or city prisons on four previous occasions for crimes including robbery and weapons possession. It was unclear why he was released in the previous cases.

The office said the case of the Monday killing would be turned over to a judge, who could order the man held at a detention or treatment center for as long as 50 years.