Twenty-eight-year-old Hamin E., a homeless man from Hamburg, had only arrived in Berlin two hours before the fatal event, newspaper BZ reported on Wednesday.
Passengers on the platform grabbed Hamin, an Iranian national born in Germany who has lived his whole life in the northern port city, after he approached the young woman from behind and suddenly shoved her onto the tracks as a train arrived.
The driver was unable to brake in time, but the other people held the perpetrator until police arrived on the scene.
Hamin is well known to authorities in Hamburg, having served two years and nine months in jail for serious bodily harm and robbery after stabbing another man in 2002 when he was aged only 14. He also has a history of drug abuse.
Berlin prosecutors' spokesman Martin Steltner confirmed to The Local that Hamin had been transferred to a psychiatric clinic on Wednesday evening, saying that "he definitely appears to have reduced responsibility" because of mental health problems.
Swedish media jumped on the story after it emerged that the young victim had links to the Nordic nation.
A spokesperson for the Swedish Embassy in Berlin told The Local on Thursday that she had been living in Berlin and had both Swedish and German citizenship.
The Swedish Church (Svenska Kyrkan) told newspaper Aftonbladet that it would open its doors to any Swedes living in Germany who were concerned about the woman, who has not been publicly named.
"We have laid out our emergency number on Facebook and we are open all day and evening," said its rector Lena Brolin.
She said that the church wanted to make sure that Berlin's Swedish population had access to information and support.
"Especially in a crisis, it is important for many to talk about what happened in their own language."
Maddy Savage contributed reporting